A Scoping Review of Stress Measurements and Psychometry in Police Research

Despite a growing body of research, there is no systematic body of evidence that establishes the rigour of existing measures of stress among police. The aim of this scoping review was to investigate (1) the diversity of stress measures used in police research and (2) the psychometric properties of such measures and the ways in which they are utilised. The systematic literature search discovered 16,216 records, which were reduced to 442 records of relevance. A total of 20 qualitative and 422 quantitative studies were found to be relevant, including a total of 129 unique measures, of which the majority showed satisfactory reliability (Cronbach’s alpha ≥ 0.80). The identified measures pertain to four main categories: police-specific, perceived stress, psychological and physiological outcomes (including mood and affect changes), and assessment batteries. The measures have a general tendency to emphasise illness, and police-specific stressors pertain mostly to traditional police work. Measures should be chosen based on the aspect of the stress phenomenon that is to be investigated. This study provides detailed recommendations concerning how to use these measures to advance research concerning stress among police.

or as a civilian (Alderden and Skogan 2014;Ermasova et al. 2020), is no exception to this rule. The prevalence of stressrelated problems is higher among employees in the police service than among members of the general public (Morash et al. 2006;Slate et al. 2007;Violanti et al. 2013a, b). The recognition that policing is a hazardous and stressful profession has stimulated a variety of studies focusing on the relationship between stress and pathology, which have been conducted with varying research designs and measurement methods (Abdollahi 2002;Queriós et al. 2020;Webster 2014).
Police work affects society and citizens as a whole (Cockcroft 2020;Symonds 1972;Wilson 1978) either with an emphasis on law enforcement or service provision. Many tasks performed by police are incident-driven, whether they are performed by a patrol unit, an investigation division, or by the administration. The tasks are also visible, often time limited, and have no simple consensus or known solution (Anshel et al. 1997;Hansson et al. 2017). Each case and situation must be addressed in accordance with the individuals and context involved (Hesketh and Cooper 2017) either by using analytical considerations or intuitively. Irrespective of policy and practice, any use of force must be necessary, proportionate, and in accordance with human rights and equalities legislation.
Stress responses affect cognitive and motor skills, e.g., physiological requirements needed for urgent situations (Anderson et al. 2019;Anshel et al. 1997;Regehr and LeBlanc 2017;Yaribeygi et al. 2017). Employees lacking the ability to cope may pose a threat to themselves, colleagues, and the public (Saunders et al. 2019;Webb and Smith 1980) and may impair the performance of law enforcement (Bitner 2019;Shane 2020). Hence, police work and the ways in which working conditions, stress, and strain influence different facets of policing have received considerable academic attention since the early 1970s (Stratton 1978). However, a systematic overview of the rigour and properties of existing measures of stress among police is missing. This scoping review fills this gap.

Stress as a Phenomenon
A common way to understand psychological stress is through the transactional model (Lazarus 1995), according to which cognition and subsequent emotions are important considerations in behavioural response to a stimulus (Robinson 2018). Despite disagreements concerning conceptual issues and definitions in stress research, there seems to be a consensus on the importance of individual differences in responses to stressors (Anshel et al. 1997). The transactional model "highlights the cognitive process of appraisal as a mediator when confronted with a stressor" (Robinson 2018, p. 8).
Understanding personal involvement and the particular context is crucial to ameliorate or prevent stress at the workplace (Lazarus 1995). Once the appraisal process begins, the degree to which an individual considers a situation to be a source of stress depends on the subjectively perceived balance among environmental demands, contextual constraints, and resources, as well as individual coping abilities (Adams and Mastracci 2020;Dewe 1991;Lazarus 1995;McEwen 2012;Shane 2020). The appraisal process integrates two sets of forces in this context, namely, the individual's agenda and the environmental realities affecting the outcome (Lazarus 1995). Primary appraisals refer to whether the individual has a personal stake in the encounter. Secondary appraisals concern coping options based on available social and organisational resources and the amount of control that individuals feel they have over the situation. The appraisal processes and subsequent reappraisals are governed by the cumulative sum of contextual, situational, or private disturbances (Evans and Coman 1993;Gächter et al. 2011) and are a function of demands, available internal or external resources, and support (Rodrigues et al. 2019). Thus, the same situation or difficulty may be interpreted as harmless by one individual and as stressful by another (McEwen and Sapolsky 1995;Yaribeygi et al. 2017). This fact implies that situations, chronic working conditions, and daily hassles, whether acute or not, become stressful when appraised as such and not simply because they occur (Anshel 2000;Gudjonsson and Adlam 1985).

Stress in the Police Context and How It Is Measured
The various measures used to study stress among police are based on differing underlying theoretical assumptions and elements of the stress phenomenon (Dollard et al. 2013;Slate et al. 2007;Webster 2013). The measurements assess a variety of issues, such as adverse life events, stressful environments, the individual's physiological and psychological responses, and the interaction between the individual and the environment (Bhui et al. 2016). By measuring the presence and magnitude of occupational stressors, stress responses, and mood changes among police, one seeks to understand the work challenges, demands, and requirements involved in police work. The main idea is that this investigation may help to provide safe and engaging work conditions for police and to secure citizens' legal and human rights in the communities that police serve and protect.
One way of measuring stress is to inquire into policespecific stressors such as acute or chronic stressors, daily difficulties, or events of significance to policing. Another approach is to ask respondents to rate their general perception of stress. The latter approach contributes to the understanding of general and individual factors associated with perceived stress, which are not necessarily police-specific. A third way of measuring stress is to study the prevalence of reactions and outcomes, i.e., distress and strain, such as the impact on cognitive capacity, concentration, risk taking, withdrawal, anxiety, anger, irritability, and physical capacity or ailments.
Studies aimed at identifying and evaluating the general effect of occupational stress on physical and mental health, regardless of profession, seek to provide a comprehensive characterisation of work stressors in the work environment (Hurrell et al. 1998). Theoretical models have guided the construction of various generic measurements and batteries of scales. The aim of these models is to increase knowledge concerning how to foster practices that will either reduce job stress or improve an individual's adjustment to stress. Such batteries mainly contain three types of variables: work stressors, strain, and health outcomes. While comprehensive measurements may provide a more profound understanding, briefer measurements might represent an efficient first-pass psychosocial risk assessment for the identification of areas that warrant in-depth assessment and targeted risk reduction activities.
The sources of stress in the policing profession are often divided into operational and organisational demands or stressors (Hillgren et al. 1976;Kroes 1976;Reiser 1976;Shane 2020;Symonds 1970;Violanti et al. 2017), with the latter identified as the predominant stress source (Shane 2020;Stinchcomb 2004;Violanti et al. 2017). The operational demands impinging police work comprise acute (e.g., critical on-the-spot decisions, responding to high-risk calls, high-speed pursuits, missing or nonfunctioning equipment), and chronic stressors (e.g., patrol activities, inactivity and boredom, traffic control activities, help and safety duties, and the ineffectiveness of the judicial or correctional systems). Although rarer in frequency (Berg et al. 2005;Hickman et al. 2011;Padilla 2020), traumatic events and threats to physical and psychological health are also included in the category of operational demands.
Organisational stress refers to chronic (Anshel et al. 1997;Dollard et al. 2003) exposure to exacerbating and enduring pressure (Bishopp et al. 2016), including stressors such as role conflicts and ambiguity, work overload, underutilisation of skills, lack of supervisor support, bureaucratic procedures, insufficient staffing, and record keeping (Berg et al. 2006;Kop et al. 1999;Shane 2013Shane , 2020Violanti et al. 2017). In addition, stressors from the sociopolitical context of policing (Demou et al. 2020;Saunders et al. 2019;Stratton 1978) are also involved. Sociopolitical pressure refers to the ways in which employees in the police are treated and trusted by the public, media, other organisations, or family and friends (Brown 2016;Can et al. 2015;Ermasova et al. 2020;Van Hasselt et al. 2003).

Psychometric Properties
The psychometric properties of measurement instruments refer to their reliability and validity. The evaluation of psychometric properties tries to establish the scientific robustness of the scale and the assessments made (de Souza et al. 2017). As the phenomenon of stress cannot be directly observed or quantified through self-report measures, the methodological approach employs an indirect measurement design, i.e., a scale on which respondents rate their perceptions of stress-related sources or events. The indirect approach is a hypothetical construct in which a latent variable (of stress), composed of carefully evaluated and selected items, is measured.
Neither reliability nor validity refers to inherent properties of the measure but to interactions among the scales, the group being tested, and the conditions (Keszei et al. 2010). Reliability is a property of the measurement as a whole (Danner 2016) and indicates whether the measurement is consistently able to reproduce similar results across time and space (Keszei et al. 2010). Validity refers to the meaning and interpretation of the scores; do we measure what we intend to measure?
As measurements cannot be valid unless they are reliable (Keszei et al. 2010), reliability is a way of assessing the psychometric properties of measurements. Cronbach's alpha assesses the degree to which a scale or composite is consistent, whether internally or temporally, in measuring variation in a sample (Edwards et al. 2021) and represents one way, among others, to assess reliability. Known discussions of the limitations of the use of Cronbach's alpha compared to other methods are its assumptions of uncorrelated errors, tau equivalence, unidimensionality, and normality (Trizano-Hermosilla and Alvarado 2016). Nevertheless, Cronbach's alpha is the most commonly used reliability index (McNeish 2018;Peterson 1994;Raykov and Marcoulides 2019). The expression of alpha, a number between 0 and 1, indicates higher consistency with a higher score. Although universally accepted norms seemingly are lacking, Nunnally's (1978) recommendations that acceptable levels of reliability are ≥ 0.70, ≥ 0.80, and ≥ 0.90 for preliminary, basic, and applied research, respectively, have been widely applied.

Aims of the Study
Despite a growing body of research into the concept and measurement of stress among police (Cohen et al. 2019;Webster 2014), there is no systematic body of evidence that establishes the rigour of existing stress measures and their psychometric properties. In a police setting, a lack of knowledge concerning the utility of existing stress measures hampers the development of the research field as well as the possibility of promoting wellbeing and preventing ill health (Slate et al. 2007). This study establishes the rigour of existing and applied measures of stress among police by conducting a scoping review that investigates (1) existing stress measurements in the context of the policing profession and (2) the psychometric properties of such measures. In this study, we employ an acceptable Cronbach's alpha score to express a measurement's ability to detect and systematically investigate the type and form of stress that it is assumed to measure when applied to the police.

Procedure
Research into stress among police is characterised by a plethora of definitions, measurements, and methods. A scoping review approach allows openness to stress as a concept and to study designs (Tricco et al. 2018). As our aim is to map and summarise existing measurements of stress among police, the criteria for choosing a scoping review approach were fulfilled (Munn et al. 2018;Peters et al. 2020Peters et al. , 2015.

Search Methods
The first and second authors (LR and BB) planned the study and decided on search terms. The PICO approach (Schardt et al. 2007) was used in discussions with two librarians (HS, the fourth author, and ATK). Databases were chosen to investigate the literature (i.e., articles that we call records in the following) published in the fields of medicine, psychology, law enforcement, and science in general. HS and ATK planned and conducted searches from the inception of the project to June 2019 without any restrictions in MEDLINE (Ovid), Embase (Ovid), PsycINFO (Ovid), AMED (Ovid), The Cochrane Library (Wiley), CINAHL (EBSCO), Academic Search Premier (EBSCO), Criminal Justice Abstracts (EBSCO), International Security & Counter Terrorism Reference Center (EBSCO), and Scopus. The searches pertained to subject headings (where applicable) and to words in the text concerning police and law enforcement, combined with terms for perceived stress, work-related stress, demands, requirements, or working conditions. For complete search strategies, see the Appendix. All search results were exported to EndNote, and duplicates were removed.

Inclusion and exclusion criteria
Criteria for inclusion were first and foremost that the record included a measurement or an inventory tool pertaining to stress that was applied in a police setting. Both qualitative and quantitative studies were included, as measurements may be applied in both. The inclusion and exclusion criteria are reported in Table 1.

Screening Process
The first two steps in the screening process used the internet and the mobile tool Rayyan (Ouzzani et al. 2016). In the screening process, we restricted inclusion to English or Nordic languages only. See Fig. 1 for a flow diagram describing the process based on the PRISMA procedure (Moher et al. 2009).
Rayyan was used by two reviewers to screen the same records independently before comparing the results. This procedure was used to ensure transparency, clarity, and traceability throughout the selection process. LR performed the initial screening process, assessing titles and abstracts. This process reduced the number of eligible records from 16,231 to 2191. The second part was organised in five waves, which were completed in pairs by LR alongside either BB, KIF (the third author), or BL (the final author) using the blind mode of Rayyan. Between every wave and before starting the next wave, each pair completed dialogues to resolve conflicting decisions. This procedure contributed to the task of establishing interrater reliability for each pair and wave. The number of conflicting decisions decreased from 15 to 6%. Records judged as possibly relevant based on titles and abstracts (n = 956) were read in full.

Data Extraction
Based on 956 records, a total of 20 qualitative studies and 422 quantitative studies were found to be relevant. From the included studies, measurements of subjective stress among employees in the police and the psychometric properties (i.e., Cronbach's alpha) of such measurements were extracted.

Results
This scoping review investigates (1) existing stress measurements in the police context and (2) the reliability of such measurements as measured by Cronbach's alpha. The 20 qualitative studies provide insight into the early establishment and identification of the factors that contribute to police stress (Kroes et al. 1974a, b;Wexler and Logan 1983). However, the qualitative studies did not include measurements of stress in the form of closed questions or checklists and were therefore excluded from further analyses.
Based on 422 quantitative studies, we identified that 129 unique subjective measurements of stress had been used in police research. Within this group, 89 measurements reported psychometric properties (Cronbach's alpha), which ranged between 0.16 and 0.96. A slight majority (54%, n = 70) of the measurements reported a Cronbach's alpha score over 0.80, indicating satisfactory reliability among the police population.
The measures were divided into four major categories based on the ways in which they predominantly examine and target different aspects of the police stress phenomenon: police-specific (46 measurements, Table 2), perceived stress (23 measurements, Table 3), psychological and physiological outcomes as well as mood and affect (30 measurements, Table 4), and assessment batteries (30 measurements, Table 5). The four categories overlap in certain respects (e.g., common features concerning how stress is measured) and differ in terms of conceptual issues and national contexts of development and application. Most measures also seem to be combined when applied to the police. For example, police-specific measures are applied in combination with one or more measures from one of the other main categories.
The measurements are arranged chronologically based on when they were first developed. Information concerning at least one study in our material in which the measure was used, as well as information concerning any revised versions, are included. The tables list, from left to right, the name of the measurement, its abbreviation, the name of the developer(s), and the measurement's years of development     Revicki et al. 1993;Gershon et al. 1995;1999, cited Table 2 includes 46 unique police-specific measures, all of which include a greater or lesser number of the two primary stress sources affecting police employees: operational and organisational stressors. About half of the measurements (n = 22) indicate satisfactory reliability (> 0.80) among the police population. Measurements based on lists of events and situations such as 'Sources of acute stress' (Anshel et al. 1997) or 'Policing Event scale' (PES) (Brown et al. 1999) do not provide reliability estimates. Such scales are considered formative, which implies that high correlations among items are not expected. Experiencing one event does not increase the probability of experiencing another. In all the measurements, respondents were asked to rate the severity and/or frequency of the included stressors or situations.
Police-specific measures are characterised by a desire to capture the stress of a demanding occupation in which individuals face increased challenges and changing roles in their work. The measurements differ in terms of how they are constructed. Some measurements (e.g., 'Police Stress Questionnaire' (PSQ) (Biggam et al. 1997), 'Police Daily Hassles Scale'/ 'Police Daily Uplift Scale' (PDHS/PDUS) (Hart et al. 1993;Kanner et al. 1981), and 'Police Stress Questionnaire-Operative'/ 'Police Stress Questionnaire-Organisational' (PSQ-Op/PSQ-Org) (McCreary et al. 2017;McCreary and Thompson 2006) organised stressors into two scales in which operational and organisational stressors are measured as latent variables. Other measurements, such as the 'Occupational Stress Inventory' (OSI) (Dharmangadan 1988), 'Police Stress Survey' (PSS) (Martelli et al. 1989;Padilla 2020;Patterson 1992;Slate et al. 2007;Spielberger et al. 1981;White et al. 1985), and 'Police Stress Questionnaire' (PSQ) (Wang et al. 2014), include subscales inside the two segments in a manner similar to multidimensional assessment batteries (see Table 5). In the operational segment, we find questions of physical and psychological danger, dealing with domestic violence, and equipment issues.
Overall, police-specific stress measurements have been developed for a variety of purposes ranging from development programs, e.g., the 'Policing Event Scale' (PES) (Brown et al. 1999), 'Police Stress Inventory' (PSI) (Pienaar and Rothmann 2003;Pienaar et al. 2007) and PSS (Martelli et al. 1989;Padilla 2020;Patterson 1992;Slate et al. 2007;Spielberger et al. 1981;White et al. 1985), predicting employees at risk, e.g., 'Police Perceived Stress Survey' (Laufersweiler-Dwyer and Dwyer 2000) or 'Law Enforcement Officer Stress Survey' (LEOSS) (Can et al. 2015;Van Hasselt et al. 2008, estimating average work distribution, e.g., 'Daily Perceived Stress Level' (Korre et al. 2014), to improving knowledge concerning how to cope, e.g., 'Sources of acute stress' (Anshel et al. 1997). Table 3 includes 23 measurements assessing perceived stress. Among this group, 48% (n = 11) reported an alpha score over 0.80. Measurements in this category contain questions in which respondents are explicitly asked about perceived or experienced stress in general, at work, or in specific settings.  Some measurements are constructed to assess the perception of overall occupational stress. Typical items could be 'I feel a great deal of stress because of my job ', 'When I'm at work I often feel tense or uptight' or 'I feel pressured', for example, in 'Occupational Work Questionnaire' (OWQ) (Caplan et al. 1975), 'Measure of Occupational Stress' (Haarr and Morash 1999;Morash et al. 2006;Morash and Harr 1995), and 'Subjective Stress' (Motowidlo et al. 1986;Young 1994). Other measurements examine overall, global stress, not necessarily stress linked specifically to work, with items such as 'How often have you felt that you were unable to control important things in your life', 'In the last month, how often have you been upset because of something that happened unexpectedly', or 'In the past year, how would you rate the amount of stress in your life', e.g., 'Perceived Stress Scale' (PSS-14, PSS-10) (Cohen et al. 1983;Cohen and Williamson 1988;Graf 1986) and 'Personalized Assessment of Stress Scale' (PASS) (Anson et al. 1997). Table 3 also includes measurements assessing experiences of life events such as the death of a loved one, marital issues, and economic difficulties, e.g., 'Stress Appraisal Measure' (SAM) (Anshel et al. 1997;Peacock and Wong 1990), 'The Social Readjustment Rating Scale' (SRRE) (Collins and Gibbs 2003;Holmes and Rahe 1967) and 'Schedule of Recent Experiences' (SRE) (Burke et al. 1984) and acute stress experiences, e.g., 'Chronic and Episodic Stress' (Anson and Bloom 1988), 'Measure of Occupational Stress' (Haarr and Morash 1999;Morash et al. 2006;Morash & N. Haarr, 1995), and 'Screening Scale of Chronic Stress' (SSCS) (Strahler and Ziegert 2015). Table 4 includes 30 measurements. The measurements in this category investigate the presence of stress through impairment of functioning due to common types of psychiatric, physiological, or behavioural symptoms or mood changes resulting from prolonged or acute stress exposure among police employees. Sixty-three percent (n = 19) of the measurements reported Cronbach's alpha score over 0.80. Horrors from the world wars contributed to the growing scholarly agreement concerning a strong relationship between exposure to stress and the subsequent onset of various forms of illness. Additionally, studies conducted during the 1960s identified personal and situational factors mediating the extent of illness.

Discussion
This paper aims to provide an overview of existing and applied stress measures among employees of the police, as well as an overview of the rigour of these measures. According to the scoping review, 129 unique subjective measurements have been used to assess stress among police (see Tables 2, 3, 4 and 5), and these measures appear to work well, with a slight majority of measurements having Cronbach's alpha over 0.80.
One hundred twenty-nine measurements represent four categories that address different aspects of stress as a phenomenon and the transactional framework of stress. The first category is police-specific, followed by perceived stress, psychological and physiological outcomes (including mood and affect changes), and assessment batteries. Combined, these categories illustrate different assets of the complex interactions among stimuli (i.e., stressors referring to conditions causing subsequent reactions), appraisals of stress (i.e., an individual's perception of and relationship to stressors), and responses in the form of outcomes and mood changes. As a result, these categories highlight different parts of the transactional model. Robinson (2018, p. 6) noted that 'the delineation of stress into primary and secondary appraisals has moved stress research away from the purely physiological exploration of stimulus and response in the 1960s and 1970s and more towards cognitive mediation involving numerous factors and feedback loops'. Combinations of measures may improve the study of stress among police by allowing researchers to investigate the ways in which the cognitive process of appraisal acts as a mediator when confronted with a stressor (Robinson 2018). This approach may enhance the current situation, as some researchers have argued that studies of stress among police mainly focus on the nature of stressors without interpreting their results through a theoretical framework of stress (Rodrigues et al. 2019).
Items assessing severity are tightly connected to emotional reactions. This makes it possible to deduce the type of appraisal being produced (i.e., positive-benign, harm-threats, or challenges). Questions of frequency that correspond to the cumulative sum of contextual, situational, or private disturbances further inform the appraisal process. Researchers must examine respondents' personal experiences concerning both the frequency and perceived severity of encounters to interpret the corresponding appraisals (Evans and Coman 1993). According to Anshel et al. (Anshel et al. 1997, p. 349), the primary appraisal dimensions and perceived stressfulness explained more variance than the secondary appraisal scales and the reappraisals. As a result, examining the meaning that individuals attribute to different events contributes to knowledge concerning how secondary appraisals are associated with an individual's overall perceptions of stress. Hence, subjective perspectives, experiences, and perceptions of stress are critical to making long-term contributions to the research concerning work stress.
To summarise, the four categories of measurements complement one another. Police-specific measurements are derived from concrete occupational demands and events and gauge the major operational and organisational occupational requirements of policing. The other three categories focus on general and cross-occupational working demands and outcomes. Because general workplace problems account for a great deal of perceived job stress (Liberman et al. 2002), selected scales from comprehensive and multidimensional assessment batteries often contribute points of overlap and elaborations that are useful in studying working conditions among police. Furthermore, a measurement of perceived stress is often added to capture respondents' experiences of general work-related issues and overall stress in life.
Measurements of psychological and physiological outcomes, including mood and affect changes, are used to verify the presence of stress through various reactions or to examine outcomes or mood and affect changes. However, symptoms may have multiple causes, so scales of this kind have shortcomings in regard to interpreting associations and causalities, e.g., according to Gotts and Cox (1988), quoting Mackay et al., mood changes are frequently conflated with stress in the literature (Ermasova et al. 2020).
The majority of measurements in our results are used to assess chronic stress. Measuring acute stress is more difficult and is often conducted through artificial scenarios (Arble et al. 2019;Larsson et al. 1988;Taverniers et al. 2011). When performing simulated stressful tasks, respondents know that no serious consequences will result. Consequently, it is difficult to assure the accuracy of measuring stress originating from the task (Bertilsson et al. 2019;Brisinda et al. 2015). Acute stress is frequently assessed using biomarkers (e.g., saliva, heart rate, blood serum) combined with other measurements (Sandvik et al. 2020). However, both biomarkers and subjective measurements have shortcomings. Regardless of the choice of methods, individual motivations (Ghazinour et al. 2021) and situational cues strongly affect performance, outcomes from biomarkers, and responses (Giessing et al. 2019). It is therefore essential to ensure the ecological validity of the method applied.

Generic or Specific Measurements
Altogether, measurements from the four categories provide four points of entry to studying stress among police. However, our findings show that most measures are combined when applied to the police. In other words, police-specific measures are applied in conjunction with one or more measures from one of the other main categories. One of the reasons for this combination may be that existing measurements of stress among police include both generic and policespecific measures. Generic assessment batteries, more than police-specific measurements, have evolved in response to generally new knowledge and changes in contextual factors in workplaces (Bliese et al. 2017). Using various types of measurements is a strength, as doing so connects stress among police to the general stress literature, which provides a vital occupational context. Measurements and subscales from different categories possess complementary properties and may successfully be used in conjunction and combination.
Perhaps due to our choice of search terms, most measurements we identified are directed at the negative health effects of stress. With a few notable exceptions (Hart et al. 1993;Kop et al. 1999), most stressors in the measurements we have found appeal to harm-threat appraisals rather than positive-benign and challenging appraisals. Nevertheless, stress has both positive and negative effects. As demonstrated by the upwards slope of the inverted-U curve, positive linear theory views stress as motivating and challenging, whereas the downwards slope follows the negative linear theory, which holds that stress at any level is harmful and reduces performance (Gaines and Van Tubergen 1989). This primary emphasis on detrimental effects may hamper the possibility of gaining more knowledge into job factors that promote and sustain positive forms of stress in policing work (Hart et al. 1994). Larsson et al. (Larsson et al. 1988) found officers to perceive situations as challenging more often than they perceived them to be threatening, suggesting that situations were perceived as controllable or solvable, thereby allowing officers to remain task oriented, confident, and alert. Hence, it would be inappropriate to assume that employees of the police always experience negative stress simply due to exposure. Therefore, conclusions are not straightforward and have several interpretational pitfalls. The identification of positive and negative aspects of work is invaluable for attaining a broader picture that informs both employees and employers of areas on which to focus for improving work conditions and suggesting subsequent interventions (Bakker and Schaufeli 2008;Juniper et al. 2010;Karanika-Murray et al. 2009).
Operational stressors in measurements of policing are mainly the result of police work in the form of physical exposure to citizens, the use of force, and the sense of working with a strong possibility of violence, dangerous events, or death. Notably, most operational stressors result from the aspects of policing that are performed in the streets, i.e., 'real police work' (Reuss-Ianni 2011). This fact remains true even though police work encompasses a wide range of police-specific operational tasks that are demanding in other ways (e.g., preventing and investigating cybercrime, human trafficking, or meeting people undergoing crisis). It may seem that existing police-specific measures support a somewhat outdated narrative concerning police stress. Police-specific measures of stress may profit from a better alignment with the status quo of modern police work in their region of application. It is worth noting that the growth of professional policing worldwide has been accompanied by an increasing number of civilian employees who lack police education (Adams and Mastracci 2020). Regardless of educational background, police employees also collaborate and participate in multiagency efforts, for instance, in online policing (e.g., investigations of sexual abuse and dating fraud).
Studies concerning police stress have repeatedly documented the fact that the most frequent and stressful job factors are related to the overall organisation of work salient to all staff (Shane 2020). Such general working conditions have an impact on the majority of police employees, regardless of the work tasks performed, such as real-life or virtual patrolling, investigative work, contact or dispatch personnel, and counselling or managing (Brown et al. 1996;Galbraith et al. 2021;Kirkcaldy et al. 1998). Police services, like the public sector in general, face heightened demands for efficiency and transparency (Andersson and Tengblad 2009). Detrimental ways of organising work are found across occupational settings and are not unique to police work (Bliese et al. 2017;Pagon et al. 2011). Therefore, combining policespecific measurements with general measures of stress may be beneficial when applied to the police. Furthermore, such practice allows for the comparison of results across occupations, which is critical for developing the occupational stress research field (Evans and Coman 1993).
Adapting to the changing societal context of the contemporary world is a key driver in professionalising the police (Cockcroft 2020). This exceedingly complex process causes multiple reforms in police organisations worldwide. The changes have implied a growing need for competence, skills, and expertise (e.g., in social sciences, technology, or languages) that are not necessarily covered by ordinary police training and education (Bjørgo and Damen 2020). Additionally, with the emphasis on the competence needed to perform multiagency policing efforts, it is also anticipated that police services will increase their number of employees with other educational backgrounds, including at the police executive level.
Stressors change as areas of responsibility, roles, and tasks in the police are altered. As Brown et al. (1996) note, rank is an important variable, with staff in supervisory positions showing distinctive patterns of exposure and experience of stress compared to junior officers. Consequently, it is predicted that junior officers report higher levels of operational stress and lower levels of management organisational stress than senior staff. While some police employees perform their work tasks in highly polluted environments, in extreme heat, or in areas with dangerous animals (e.g., traffic police, environmental crime police, border police), other employees increasingly patrol and investigate, whether on or off the internet, highly emotionally demanding environments (e.g., online abuse of children, dating fraud, and domestic violence). The notable differences in the organisation of police work must be accounted for when interpreting the results of stress measurements among police. Models of police stressors should have some validity in terms of their capacity to discriminate meaningfully between groups of employees working in different contexts, with access to different resources, with different educational backgrounds, and in different departments in different parts of the world. With the use of police-specific measurements and assessment batteries in cooperation, police studies may reap benefits from both even though there may be considerable contextual differences.

How the Measurements Work
Psychometric properties in this scoping review were operationalised by reference to Cronbach's alpha. In this study, the measurements of Cronbach's alpha ranged from 0.16 to 0.97. A slight majority (54%) of the measures (n = 70) across the four categories had Cronbach's alpha values of approximately 0.80 or over. This fact indicates that, overall, they seem to work rather well. Furthermore, many of the observed differences they produce may be attributed to actual differences among individuals. Thus, 54% of the 129 measures seem to be consistent in their ability to reproduce similar results across time and space.
However, across the four categories, there were a few measures with low reliability scores (≤ 0.70). A low level of reliability indicates that the observed differences are contaminated by measurement error. Because measurements cannot be valid unless they are reliable, low reliability implies that these measures may not be equally effective at measuring a consistent difference in stress between individuals in the police. However, it should be noted that some of the measures may have been based on a formative scale development strategy (Diamantopoulos and Winklhofer 2001). If this is the case, Cronbach's alpha should not be used as a criterion for scale quality.
As shown in the tables, estimates of Cronbach's alpha scores differ. Reliability is not a fixed property (Keszei et al. 2010) but a function of the measurement, respondents, and circumstances under which a study is conducted. Before a measurement instrument can be used, its measurement properties, i.e., its reliability, validity, and responsiveness, should be assessed and found to be adequate.
Regardless of the assessment method, estimates of reliability should always be scrutinised for inaccuracies, as any chosen method entails biases. For example, known factors affecting the Cronbach's alpha score are its assumptions of uncorrelated errors, nonequal tau equivalence, normality, and unidimensionality (McNeish 2018).
Unidimensionality has to be verified prior to calculating Cronbach's alpha score. The reliability analysis may begin with an inspection of the factor structure. Scales that inadvertently investigate more than one construct are by definition not unidimensional and should not be measured by Cronbach's alpha. Factor loadings and latent variable modelling are increasingly common and may be warranted to measure tau equivalence and whether items vary jointly (DeVellis 2017). Usually, items in scales measure the same construct to different degrees of precision, which becomes visible through factor analysis. Furthermore, the circumstances under which the questionnaire is administered impact reliability and may cause uncorrelated errors where sources other than the construct being measured cause item responses to be related to another. While nonequal tau equivalence and normality of variable distributions cause Cronbach's alpha estimates that are too low, the uncorrelated errors affect estimates of Cronbach's alpha in unpredictable ways.
Cronbach's alpha is also dependent on scale length. Thus, irrespective of internal consistency, Cronbach's alpha will be high in scales consisting of more than approximately 15 items. In contrast, the shorter the scales, the more Cronbach's alpha reflects the correlations among the items included. Scales with a high Cronbach's alpha might be too interrelated and could indicate redundancy. New prerequisites and new findings or knowledge may change the reliability of measurements. Researchers investigating occupational stress have an imposed obligation to ensure realistic and recognisable wordings and expressions where the chosen stressors reflect the actual working context. Police-specific measurements have evolved in different parts of the world. As they reflect different work settings and conditions, modifications may be necessary before use.

Strengths and Limitations
This rigorous overview could not have been possible without a meticulous and systematic literature search. Through this search, the content and target of each measure, as well as the ways in which they operate in police settings, have been described.
A limitation of the scoping review, which may have hampered the conclusions and the recommendations drawn, is that studies in languages other than English were excluded. It is also important to note the need for awareness of the context surrounding the measures. Economic, cultural, political, and historical development affect society on both sides of the law, as do climate (Rasdi et al. 2017), geography (Ricciardelli 2018), police education (Bjørgo and Damen 2020), population, crime rate, and the number of police employees (Garcia et al. 2004). Thus, although the measures included in this scoping review are varied, they may be biased, as they predominantly portray the police in a minority of the world (e.g., Northern America and Europe). However, keeping these limitations in mind, this comprehensive review offers a representative view of measures of stress in the police.
Psychometric properties may be measured in several ways other than by Cronbach's alpha. With a broader scope of assessment, we could have included estimates of more measurements. First, single-item measurements do not provide Cronbach's alpha scores, and measurements without Cronbach's alpha scores may have been examined by other methods (e.g., by structural equation modelling, SEM, or McDonald's omega, ω). On the other hand, reliability differs as the populations and purposes of the study vary. That is, any measurement in the tables may work well and serve its purpose in the context in which it was used, independent of Cronbach's alpha indicated in the tables. Nevertheless, as Cronbach's alpha is a well-known and common way to establish rigour, it served the purpose of this scoping review, in which the aim was to gain a better overview of measurements and their psychometric properties.

Recommendations
Based on the findings in this scoping review, the following recommendations for conducting studies into stress among police are made.
First, depending on whether the aim of a study is to investigate stress among police across different categories, whether from a generic or a police-specific perspective, measures should be chosen to ensure alignment with theoretical assumptions, the aspect of the stress phenomenon the study aims to investigate, and sufficient psychometric properties.
Second, reliability scores should be evaluated before choosing a measure. In this study, a slight majority of measures had Cronbach's alpha values of approximately 0.80 or over. However, this information was not included in all the records we examined. Measurement should not be chosen based solely on reliability scores (e.g., Cronbach's alpha). We encourage all researchers to conduct reliability tests and interpret the score in light of known biases.
Third, if the aim is to investigate subjective stress experiences from a generic or a police-specific perspective, researchers and practitioners should apply one of the questionnaires that commonly ask respondents to rate the extent to which a situation or stressor is perceived (or not perceived) as stressful. These questionnaires may include police-specific measurements such as Daily Perceived Stress Level (Korre et al. 2014), 'Law Enforcement Critical Life Event Scale' (LECLES) (Coman et al. 1991b;Sewell 1983), 'Law Enforcement Officer Stress Survey' LEOSS (Can et al. 2015;Van Hasselt et al. 2008, 'Critical Incident History Questionnaire' (CIHQ) (Weiss et al. 2010), or 'Policing Event Scale' PES (Brown et al. 1999). Generic measurements could include 'Subjective Stress' (Motowidlo et al. 1986;Young 1994). Among assessment batteries, 'Work Stress Inventory' (WSI) (Barone et al. 1988), 'Occupational Stress Indicator', OSI (Evers et al. 2000;Robertson et al. 1990;Siu 2002), or the 'Job Stress Survey' (JSS) (Spielberger and Reheiser 1994) could be considered.

Implications
The main results from this scoping review show that there are a wide variety of existing measures applied to investigate stress among police. Most measures work well in the context in which they are used. It is recommended that measures be chosen based on the theoretical assumptions concerning stress as a phenomenon in the study in question as well as on the extent to which such measures suit the context and aims of the planned study. It is also advised that measures be chosen to develop both generic and police-specific knowledge. As there seems to be an emphasis on patrolling police work stressors in the context of police-specific stress measures, these stressors may profit from more alignment with the status of (on and offline) police work from several parts of the world to better measure the status quo. More research into stress among police, regardless of police employees' educational background, is also encouraged. More focus should also be devoted to the measurement of stress and wellbeing. Well-chosen measurements can improve the study of stress among police and thereby improve police work and the effect of policing on the societies that police protect and serve.  (stress* or workload* or work load* or demand* or requirement* or strain or straining or strained or ((operational or organisational or organizational) adj3 (work or job or task* or duty or duties or activit* or factor*))).
Number of hits: 8179.
Acknowledgements The authors thank Anders Tveit Klette (ATK) for his assistance in the literature searching process. We also want to thank all the librarians working at the Norwegian Police University College who have been priceless at helping us finding articles in full text.
Author contribution LR and BB planned the study and decided on search terms. HS and ATK conducted the systematic literature research and composed the appendix. LR, BB, KIF, and BL analysed and interpreted the data. LR was a major contributor in writing the manuscript and preparing figures and tables. All authors read and approved the final manuscript.
Availability of data and materials All data relevant for this study are included in this published article.

Declarations
Ethics approval Not applicable.

Competing interests
The authors declare no competing interests.
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