Nowadays, a growing number of employees, mainly knowledge workers, have control over their working hours, indicating that they have the opportunity to decide themselves when to stop working . Additionally, the frequent use of mobile devices such as cell phones and laptop computers makes it possible to work at alternative workplaces, such as at home  or in airport lounges . At the same time, restructuring and downsizing have led workers to cope with a higher workload [4, 5]. Consequently, in many occupations work is never completely finished at the end of the day. While many people do not find it difficult to put their work aside after office hours, more and more employees may work longer hours than they actually have to .
It can be argued that a distinction can be made between two different types of chronically hardworking employees. One group is labeled as workaholics, whereas the others are referred to as work engaged employees . To date, few studies have looked specifically at the difference in work motivation between workaholics and work engaged employees. It is relevant to distinguish between workaholism and work engagement, since apparently, as we will argue later, similar work behaviors lead to opposite outcomes. A better understanding of the mechanisms underlying workaholism and work engagement might facilitate the implementation of more timely and appropriate interventions for enhancing healthy work behaviors. Therefore, the current study aims to gain insight in the motivational difference between these two types of employees.
Oates  coined the term workaholism to refer to persistent work behavior. Ever since, scholars have started to examine workaholism, which has led to different points of view on its origin and characteristics. For instance, some hold a negative view of workaholism [8, 9], whereas others also emphasize its beneficial elements [10, 11]. Similarly, some suggest that workaholism consists of a compilation of personality traits , whereas others think of it as learned addictive behavior . In spite of the disagreement, Scott et al.  concluded that the vast majority of scholars commonly define workaholism as consisting of two elements: (1) the tendency to work long hours, whereas at the same time (2) having a strong inner drive to work. In concordance with Schaufeli, Taris, and Bakker [14, p. 219], we therefore define workaholism as “an obsessive, irresistible inner drive to work excessively hard”.
Alternatively, an enthusiastic involvement in work, also called work engagement, could also explain why some employees work persistently. According to Schaufeli, Salanova, González-Romá, and Bakker , work engagement refers to a positive, fulfilling, work-related state of mind, which consists of three dimensions. These dimensions are vigor (having high levels of energy), dedication (being strongly involved in one’s work), and absorption (being completely engrossed in one’s work). Empirical investigation  has shown that the dimensions vigor and dedication are the opposites of the two central dimensions of burnout, exhaustion, and cynicism, respectively . Also, vigor and dedication are considered the core characteristics of work engagement [18, 19]. Therefore, absorption is not taken into account in the current study. In addition to job resources [20, 21], individual factors such as trait competitiveness , proactive behavior , and self-efficacy  have been found to be significantly associated with work engagement.
It seems difficult to distinguish the concepts of workaholism and work engagement because, at first glance, the work behavior of workaholics and work engaged employees seems to be similar. However, when considering the two concepts more closely, several differences become apparent. Workaholism is related to unfavorable outcomes, such as self-perceived ill-health  and poor emotional wellbeing , whereas engagement is related to desirable outcomes such as personal initiative  and job satisfaction . Hence, we do know that workaholics and work-engaged employees differ from one another , but we do not know why they are different. One plausible explanation for the distinction between “workaholism” and “work engagement” may be a different underlying motivation to work excessively. To date, no theory or model exists that addresses this assumption.
In the present study, we introduce an explanatory paradigm that stems from the field of clinical psychology, called the mood as input (MAI) model . This model has shown to be relevant in explaining persistence in the area of clinical psychology, for instance depressive rumination . The MAI model assumes that people use personal cognitive rules to estimate how they are doing on a given task with no clear ending. That is to say, on the one hand, individuals may evaluate their progress towards a goal by considering how much they have done and on the other hand they may estimate their progress towards a goal by evaluating their current enjoyment in performing the task. Such rules for deciding on what basis to stop or continue are labeled “stop rules”.
The MAI model also postulates that individuals use their current mood as information for how to act in response to these stop rules. For instance, when evaluating whether one has done enough (i.e., the enough stop rule), a positive mood is interpreted as being satisfied about one’s performance, meaning that it is all right to quit the task. However, a negative mood would convey that one is not yet satisfied, implying that one has to continue in order to feel content. However, when assessing one’s task enjoyment (i.e., the enjoyment stop rule), a negative mood would notify that one no longer enjoys the task, leading one to quit the task. On the other hand, when considering one’s task enjoyment, a positive mood would be interpreted as intensely enjoying the task, resulting in persistence.
To summarize, the information that the specific mood state conveys is dependent upon the stop rule used. Martin et al.  successfully conducted several experiments to test this assumption. For example, after a positive or negative mood induction, participants were instructed to read about behaviors of a target person to form an impression of that person. Half of the participants were instructed to continue reading the information until they collected enough information to form an impression of that particular person. The other half of the participants were told to continue reading the information as long as they enjoyed the task. The results showed that when given an enough stop rule instruction, participants in a negative mood continued longer as compared with participants in a positive mood. Conversely, when appointed an enjoyment stop rule instruction, participants in a positive mood continued longer than participants in a negative mood.
Building on these findings, MacDonald and Davey  applied the predictions of the MAI model to explain a core characteristic of obsessive–compulsive disorder, which is compulsive checking. Congruent with the MAI hypothesis, MacDonald and Davey found that either a positive or a negative mood can lead participants to stop or continue checking, depending on the interpretation of their mood. Particularly, the combination of a negative mood and the enough stop rule resulted in prolonged persistence. This finding seems to provide a plausible explanation for the compulsive behaviors of obsessive compulsive checkers.
There are several indications that these findings may also be relevant to the study of workaholism. Firstly, workaholism has been associated with obsessive compulsive personality traits . Furthermore, it seems that workaholics continue working by meeting self-imposed deadlines [10, 13]. They have an “endless pursuit of more and more accomplishment” [31, p. 435]. More specifically, it is suggested that compulsive behaviors such as workaholism arise when individuals commit to self-imposed and rigid personal rules . Considering that they are assumed to take pride in the amount of work they have done , workaholics seem to use an enough stop rule that drives them to work persistently. It has also been established that workaholics commonly experience negative affective states. Robinson  found, for instance, that workaholism is related to anxiety. Likewise, Burke and Matthiesen  revealed that workers with a compulsive drive show increased negative affect, whereas Porter  argued that workaholics may work to avoid their negative feelings. Building on the MAI hypothesis, we expect that workaholics use their negative mood as input for an enough stop rule, meaning that a negative mood in combination with the enough rule is related to workaholism.
The MAI model appears to be also suitable to provide an explanation for work engagement. Work engaged workers are likely to employ a different internal norm for deciding when to stop working. Schaufeli et al.  argue that work engaged employees work long hours because work is satisfying to them. Because engaged employees are intrinsically motivated to work , it is likely that these employees continue working as long as they enjoy their work. How long engaged workers find their work enjoyable enough to continue working may be dependent on their level of positive mood. In accordance with this assertion, Schaufeli and Van Rhenen  found that positive affect is related to work engagement. Likewise, Burke and Matthiesen  observed that work-engaged employees (“work enthusiasts”) showed more positive affect than workaholics (“work addicts”). We therefore expect that work engaged employees use a positive mood as input to an enjoyment stop rule, suggesting that particularly a positive mood in combination with the enjoyment rule is related to work engagement.
The present study was conducted in order to examine to what extent the MAI model can be fruitfully applied to investigate the motivational underpinnings of workaholism and work engagement. Since we are not aware of a scale that assesses stop rules in the work context, the goal of study 1 was to develop and test a scale for the measurement of work stop rules. In study 2 the factorial validity of the scale was further examined. A second aim of study 2 was to investigate if mood, stop rules and the interaction between mood and stop rules predict workaholism and work engagement.