Why is pet goods consumption imperceptible for economists? A scoping review

Nowadays, pets more frequently are becoming family members which deserve certain products and goods, as well as services. In this way, pets are becoming consumers even they do not have a possibility to make decisions (as opposed to human being) as we analyze taking into account human being. Recently pet-related topics are gaining more attention in the press and among researchers in the field of marketing and psychology. Numerous articles regarding pet-related business patterns, like pet insurance, day care and pet friendly hotels are published. No wonder, the popularity of pets among households has been growing for many years. In this article, a scoping review aimed at identifying available studies about expenditures on pet goods and owners’ economic consumption choices has been conducted. A comprehensive search strategy was used across Scopus and EBSCO database. The results show that there is only a few studies concerning pet goods consumption through the lens of economic theories. As such this topic in not explored enough while the market of goods and services is growing.


Introduction
These days, about 67% of American households own a pet. The number of US households with pets increased from 66.50 million to 84.90 million between 2012 and 2020, and the this upward trend will continue (APPA 2021).
Many pet owners feel not like a pet owner but like a pet parent. In this way, the phenomenon of pet parent shows that people do not regret spending money on their 'babies'. It's no wonder that 83% of pet owners identify to themselves as "Mommy" or "Daddy" (Morais 2004).
Pets become new members of the family and should be considered in the economics of household in the same way that other members of the family are. Household animals thrive in today's culture due to contemporary lifestyles such as maternity leave, flexible working hours, and later marriage. Furthermore, COVID-19 is expected to increase the popularity of owning pets (Oliva and Johnston 2021;Giansanti et al. 2022).
While the economics aspects of the family/household might stretch out to pets, as confirmed by regular references to pets as "child" there are various differentiations among pets and kids: it is legitimate to purchase pets, yet not kids; undesirable pets can be deserted; and pets cannot accommodate guardians in their advanced age. Single people can possess pets without the shame that accompanies being a solitary parent. Pets have additionally stood out enough to be noticed in legal strategies until of late.
The worldwide pet goods market value has been growing systematically for last 10 years, reaching the value of USD 138.24 million (including the value of the pet food market-USD 98.07 million and the value of pet products-USD 40.18 million) in 2020 (GMID 2022) (Chart 1). Here, the pet goods market includes of: the pet food market, the cat litter market, the veterinary services market, the pet supplements market, and the market for other pet products. This value increased by 42% compared to 2010 (including the value of the pet food market by 38% and the value of the pet products market by 52%) (GMID 2020). The number of pets in the world has also been increasing systematically since 2010. Over the past 10 years, the population of domestic animals, i.e., cats, dogs, aquarium fishes, domestic birds, small mammals and domestic reptiles, has increased by 29% in 2020 and amounted to 4,952,320,000.72 (GMID 2022). Just in the UK, in just one year, an average, weekly households' expenditure on pet goods consumption household rose by 675% from £ 0.80 to £ 5.40 (Office of National Statistics 2017). While in US, expenditures connected with pets amounted up to 1% of total households' expenditures and were higher than average expenditures on alcohol, stationary phone payment and men and children clothes and an average yearly expenditures of households on pet food were higher than average expenditures on sweets, bread and poultry (Henderson 2013) (Fig. 1).
As such, this is no longer a service niche, dominated only by small aquarium shops as it used to be 20 years ago (Frątczak-Rudnicka 2015;GMID 2022). Nowadays, this market consists of: veterinary clinics, toys and accessories (including electronic gadgets), pharmaceuticals, clothes, professional literature, TV channels and internet portals for pets, and even cemeteries for animals. The more sophisticated market of pet services is also gaining importance: cosmetic, hairdressing, dietary or hotel services (Frątczak-Rudnicka 2015). Taking into account that this market is growing it has to be noticed that the economic literature has to be somehow recognized the way how the pet consumption is described, analyzed and as well developed with conclusions which can contribute to the research and also implications for this business.
The paper's aim is to present the results of scope review in which the main question asked was: in what way and what new findings could be found in the literature when we would like to analyze the pet consumption especially expenses on pet goods and pet owner economic choices? Shortly, the aim was to see if and how the link to the economic literature of this consumption is presented in available publications. Two detailed research questions were added: -Are there any studies that analyze pet goods consumption through the lens of economic theories? -And which economic theories are included in studies concerning pet goods consumption and how they are presented?
In this paper, after a short theoretical context, methodology of scope review was detailed described with sum up of the results. The paper ends with conclusions and limitations.

Theoretical background
A wide range of studies related to pet goods consumption can be already found in the international literature, but those pieces are primally focused on consumer side (Archer 1997). There also researches who were focused on people's motives of owning pet (Zasloff and Kidd 1994), relations between pet and pet owner (Ellson 2008) and influence of pet owning on pet owners' health e.g., blood pressure (Karen 2003).
According to other studies pet owners consider pet as a family member, they frequently let their pet sleep in the bed with them, their pets get presents and they participate in their holiday (The Harris Poll 2012). There are even researches suggesting that pet owners treat their pets like a family member or even as a childterm known as a 'fur baby' in the American literature (Greenebaum 2004). There are many economic well-known theories and studies that cover consumer behavior and economic decisions among families with children-e. g. Gary Becker's (Becker 1976) and Harvey Leibenstein's considerations (Leibenstein 1957 In the neoclassical theory of consumer choice people make their consumption choices to maximalise utility (described by preferences) subject to an individual budget constraint. It shows how the consumers should choose if they make rational choices and use utility maximizing model (Varian 2019). For various types of goods, income and price elasticity of demand is analyzed, as well as income and substitution effects of the price changes are studied. The diminishing marginal utility is also assumed. Extensions of the basic model show how the decisions are made in a household and could be studied for different types of households.
Pet goods consumption has not been included in considerations in following economic consumption thesis as: absolute income hypothesis (Keynes 1936), relative income theory (Duesenberry 1949), permanent income hypothesis (Friedman 1957), life-cycle theory of consumption (Ando and Modigliani 1963) and conspicuous consumption (Veblen 1899). In other words, there are not economic studies that detailed explain: -If households' consumption on pet goods function is an economic formula that represents the functional relationship between total households' consumption of pet goods and households' income. -If the households' pet goods consumption decisions are motivated by "relative" consumption concerns. -If households' level of pet goods consumption depends not only on its current income but also, on its long-term expected earnings. -If households' preferences regarding pet goods are determined to the position of each individual in the social hierarchy.

Searching strategy
A comprehensive search string on 'pet goods consumption' was developed for searches in two typical for social science electronic databases-Scopus and EBSCO (Academic Research Source eJournals [EBSCO] up until March 2021). Titles first and then abstracts were checked for inclusion by two raters (NG and JPB) after an initial step of deleting duplicates and irrelevant entries. Records were assigned to reviewers at random, and conflicts were settled by consensus with a joint agreed decision about the publication. For each of the articles included in the original search, a snowball search was undertaken to find additional records for full-text inspection using Google Scholar's "related to" and "cited by" tools (Atkinson and Cipriani 2018). Additional papers based on specialist expertise on the topic of pet product use have also been added. Additional articles were found by looking through the bibliographies of the final batch of records. At the final stage of the procedure, two raters independently reviewed the full text (JPB, NG).
The following exclusion criteria were agreed to take into account: (a) other types of document: Conference Paper, book chapter, conference Review and review, (b) documents where one world connected to Polyethylene terephthalate (PET) from the following list have appeared in title or abstract or keyword: "polyethylene", "petrol", "Physiologically equivalent temperature", "plastic", "polymeric", "methyl" and (c) documents where one world connected to Positron emission tomography (PET) from the following list have appeared in title or abstract or keyword: "AAFP", "AAHA" OR "serotonine*" OR "tomography*" OR "SPECT*" OR "CNR*" OR "fMRI*" OR "tDCS*" OR "DBS*" OR "molecular*").

Publications selected for review
A total of 2405 records were retrieved based on the original search. There were 13 duplicates. 2392 records have been screened by title and most of the articles were excluded because: they were related to medical research ("PET" as Positron emission tomography, despite the exclusions in the keywords, there were many articles), they were related to environmental, chemical research ("PET" as Polyethylene terephthalate, despite the exclusions in the keywords, there were numerous articles). Based on the title screening 112 articles were identified for abstract review. Based on abstract review 97 of them have been excluded, so 15 articles found in databases were identified for full-text review. The remaining 97 articles dealt with the possession of pets in a household in a different context, not including pet goods consumption. The most common subject related to keeping a pet is the analysis of its impact on the health of the owners, mainly on the risk of asthma. Other popular topics related to pet keeping are: analysis of the mental support/well-being of a pet owner related to owning a pet, an analysis of the emotional relationship between a pet owner and a pet, an analysis of people's attitudes toward pets, and an analysis of pet owners' problems with renting an apartment. After full-text review 2 articles have been rejected-one because language (article in German) (Pütz and Poerting 2020), second because of very specific topic-prescribed consumption in case of pet goods consumption (Lamour and De La Robertie 2016). In the end, 13 articles based on the original research have been emerged. Additional 12 records were identified as potential important based on the bibliographic check of selected papers but based on abstract review 7 of them have been further excluded. Finally, this resulted in 18 records included in this scope review (See Fig. 2). Details on the characteristics of the different studies included in the review are provided in Table 1.
It is worth highlighting that most studies were conducted in English speaking, high-income countries, including Scandinavian countries, Taiwan and the United States of America, and that no studies were conducted in low and lower middle income countries. A brief sum up of the research selected for the analysis is presented in Table 2.  There is a correlation between spending on pets good consumption and spending on owners' goods. Dog owners have also been discovered to be more open to their own food costs than to the prices of their dog's food. This may be because dog food accounts for a small portion of total spending, so paying a high price for it has no effect on overall spending Koppel et al. 2018 To determine what aspects of pet food appearance characteristics determine higher liking among pet owners consists of three opposing aspect pairs: personal and social, symbolic and functional as well as attachment and control. Those consumers who regarded their pets as their self-extensions differ from other respondents and consume pet food differently than others There is a connection between seeing pets as extended self and consumption behavior in pet food. The concept of extended self does play a role in consumer behavior when it comes to pets Kylkilahti et al. 2016 To develop a conceptual understanding of coconsumption by examining how pets act as co-consumers in everyday consumption The pet owner and the pet have consuming experiences in which they engage with other actors like service providers. Pet owner consumes because of the pet and must continuously consider pet in decisions and activities other than pet consumption, such as what sort of car to buy, where to work, who to marry, and so on

Pets appear in three roles as co-consumers.
Pets as co-consumers of products, services and experiences participate in consumers' everyday life in three ways: (1) consumption because of the pet, (2) consumption for the pet and (3) consumption of the services provided by the pet Mosteller 2008 To explore the meanings and roles pets play in peoples' lives Relationship theory helps explain the drivers behind pet-acquisition growth. A consumer pet relationship framework is used to identify factors that may influence the strength and duration of consumer -pet relationships Consumers who perceive their pets to reinforce their self-concepts, elevate their social status, and be integrated members of family or social networks are associated with positive pet-human relationships. The physical proximity between the pet and consumer may positively reflect the consumer's emotional attachment to the pet  Ridgway et al. 2008 To examine how a predisposition to buy excessively for one's self connects to spending on one's pet using two research Respondents who score high on an excessive buying index also tend to spend more on their pets There is a relationship between a tendency for excessive buying and spending for one's pet. One reason for this relationship seems to be that the participants form very strong attachments to their pets and consider them to be their children

Results
The vast majority of articles concerning pets in households refer to their impact on the health of their owners (mainly on asthma) (i.e., Medjo et al. 2013;Shirai et al. 2005). The other researches (i.e., Kim et al. 2020;d'Ovidio and Pirrone 2018) are focused on people's motives of owning pet and relations between pet and pet owner. Other very popular topics concerning keeping pets in households: the mental support / well-being of a pet owner related to owning a pet and an analysis of pet owners' problems with renting an apartment (i.e., Power 2017; Chee 2017). Only a few articles concerning pet goods consumption but definitely most of them is on the marketing field. The percentages of studies grouped by the main topics have been shown in Table 3. Human-animal bond is the most popular variable in literature that has correlation with expenditures on pet goods consumption. The human-animal bond is not just between people and traditional companion animals, such as dogs and cats. People develop relationships with birds, pocket pets, reptiles, and large animals, including food production animals. Human-pet bond is the most common variable in the literature that may have an influence on pet goods consumption (Vänskä 2016;Kirk 2019;Gates et al. 2019;Chen et al. 2012). Many people believe their pets are their soulmates. Strong emotional bond between a pet owner and a pet (pet parent, coconsumption phenomena) meaning that people do not regret spending money on 'babies'. Pets live with people and participate in people's everyday life activities and they are often seen as human-like family members. Consumers from the industrialized countries are investing more money in their pets and spending more time with them than ever before. The pet with its owner can be even considered as a form of an unit that consumes together (Kylkilahti et al. 2016;Maharaj et al. 2018). Ridgway et al. (2008) proved a relationship between a tendency for excessive buying and spending on their's pet. This relationship seems to result of very strong attachments The welfare of the pet's owner 5,56% The consumption of pet goods 11,11% The relationship of children with pets 0,00% The family view to pets 5,56% Family spending on pets 11,11% The tendency to buy pets -Spending on fashion and accessories for pets 5,56% Pets insurance 11,11% Pets trademarks 5,56% to their pets and considering them to be their children. They report feelings of being better "parents" if they take care of their pets by spending excessively on them. Respondents who score high on an excessive buying index also tend to spend more on their pets for toys, food treats, clothing, accessories, and grooming products. According to Vänskä (2014) the anthropomorphized animal plays a crucial role in building and comprehending the romantic ideal of childhood and innocence. Real animals, especially small dogs, have begun to replace teddy bears and other stuffed animals as the dressed-up childlike animal, in tandem with the new educational attitude toward pets and animals in general. The same author highlighted that pet dog and human are built as a team that consumes together and has shared user experiences. Pet dog fashions show how the desire to create a bond between a person and a dog is translated into tangible products and services (Vänskä 2014). Mosteller (2008) explored the meanings and roles pets play in peoples' lives. Relationship theory helps explain the drivers behind pet-acquisition growth. According to him consumers who perceive their pets to reinforce their self-concepts, elevate their social status, and be integrated members of family or social networks are associated with positive pet-human relationships. Brockman et al. (2008) shown that consumers' emotional relationship to animals has a significant impact on the nature of their veterinary care decisions. Consumers with moderate and low attachments make cognitive and reasoned decisions. Consumers who regard their dogs as cherished others and elevate them to family-member status, even spiritual being status, make more emotional rather than logical pet-health decisions. According to Chen et al. (2012) the type of relationship that exists between pet owners and their pets can be used to create consumption value and behavior clusters. This study found that human-pet relationships have a variety of effects and that pet owners vary in terms of consumption beliefs, knowledge search habits, and retail selection preferences, using a variety of pet services. Although the most frequently cited variable influencing the pet goods consumption is human-animal bond, there are also observable variables that can determine it. Other variables that is connected with expenses on pet goods is household's income. According to Williams et al. (2020) the amount households spent on pet care rose with income. Owners with an income of more than $55,000 spent an average of $164 more than those with a household income of less than $55,000. Pet owners with a household income of more than $55,000 may be more willing/able to spend more on their pets and pet-related expenses since their disposable income permits them to spend beyond essential living needs like rent, food, and petrol. Expenses on pet care are also statistically significantly correlated with: having insurance, other expenses on pet goods (e.g., toys, feed, etc.), past pet's incidence of diseases and expected future expenses on pet care. Higher income respondents were more likely to say they had taken their pet to the veterinarian, particularly if the visit included costly emergency treatment (Gates et al. 2019). Owners with a higher income preferred more regular, more costly vet care, implying that those with more disposable income were more likely to invest in their dog's health and well-being. The probability for pet-related and veterinary service expenditures increased with income, education, and family size and was higher for household heads who were white, were married, owned their residence, and lived in a rural area (Wolf et al. 2008). According to Schwarz et al. (2007) pet expenditures are lower in households with very young children, indicating a substitution link. Pet spending is lower in households with additional children, indicating a substitution relationship. The effect of income on pet ownership and pet spending is combined in the income elasticities computation, women in married families had lower income elasticities for pet expenditures than males. As has been shown most researches who explore observable variables that determine expenses on pet goods analyze veterinary/pet insurance market. Those expenses are familiar for pet owners-28.5% owners reported having at least one pet insurance (Chaumet et al. 2021).
A wide range of studies related to pets goods consumption are primarly focused on consumer side (Koppel et al. 2018;Tesfom and Birch 2010;Jyrinki and Leipamaa-Leskinen 2005). Koppel et al. (2018) demonstrated that there are products' characteristics that may have an influence on owner's purchase decisions. Several factors influence the purchase decision of pet goods (in that article dry dog food), such as product price, packaging, brand, marketing claims, product extrinsic characteristics (aroma, appearance, color, shape, size), whether the companion animal will consume the food, and if they do, what are the digestive and health consequences. Tesfom and Birch (2010) highlighted that there is a correlation between spending on pets good consumption and spending on owners' goods. Moreover they indicated that dog owners are more loyal to dog food brands than to human food brands and dog owners have often found to be more open to the price of human food than to the price of dog food. What is more, dog owners are more committed to purchasing healthy dog food than they are to purchasing healthy human food. According to Jyrinki and Leipamaa-Leskinen (2005) there is a connection between seeing pets as extended self and consumption behavior in pet food. The concept of extended self does play a role in consumer behavior when it comes to pets. Consumers who see their dogs as extensions of themselves vary from other respondents in case of pet food consumption. Among the extended self group, price and quality awareness, pleasure providing, self-esteem, knowledge, and pet feeding planning were highlighted. Syrjälä (2016) depicted the turning point in a casual enthusiast's transformation into a serious hobbyist inside the community of dog agility devotees. According to her the enthusiast at the turning point becomes a serious hobbyist who engages with a multitude of dog-related businesses to establish his or her seriousness.

Discussion
Pet goods consumption is not the main area of interest to researchers so far. For this reason, conducting a literature review in this field was a meaningful challenge and it was confirmed by limited number of papers found and selected for this review. A reflection of the difficulties in conducting this type of analysis is, has been for example, adding as many as five articles from outside the databases (Scopus and EBSCO), which constitute almost 1/3 of all articles included in the review. The analysis is of course limited to Scopus and EBSCO but on the other hand all relevant work should be found as rather including other often used databases like: PsycINFO, ProQuest Central, SAGE Premier and Science Direct. The analysis of pet goods consumption are focused mainly on marketing field. In particular they deal with categories such as preferences, segmentation, consumer behavior which are mostly recognized to and appraised by marketing field. Researchers that study pet goods consumption do not focus on fundamental for economists topics: demand elasticities, testing the law of diminishing marginal utility, microeconomic utility etc.
Even the scope review confirmed that some of the papers accord with well-known microeconomic theories mentioned in theoretical background like absolute income hypothesis or life-cycle theory of consumption or conspicuous consumption, still there are gaps. As reference to absolute income hypothesis (J.M. Keynes) could be found in Wolf et al. 2008;Williams et al. 2020;Gates et al. 2019 but those studies have not been analyzed via economic theory lens and Tesfom and Birch 2010-this study was only linked to marketing field. In case of life-cycle theory of consumption (F. Modigliani, A.K. Ando)-here Williams et al. (2020) indicated that expenses on pet care are statistically significantly correlated with expected future expenses on pet care, but the life-cycle theory of consumption theory in case of pet goods consumption has not been analyzed in economic way in their work. And last conspicuous consumption (T.B. Veblen) found in Syrjälä (2016) shown that some dog owners manifest their pet goods consumption that going to extreme lengths in consumption and spending but there was not used economic approach. Also there are some theoretical papers like Maharaj et al. 2018;Vänskä 2014 but the aim of those literature reviews were completely different. Authors put leisure activities with pets, emotional bond between pets and owners, and transformative processes of pet consumption over expenditures on pet goods or owners' economic consumption choices.
Based on the scoping review, it is impossible to create an economic model to express the consumption function for pets and so far it was not found (via scoping review) adequate economic literature that shows the main components of consumption function for pets (owners' income and owners' expenses). Moreover, it was impossible to show a demand/supply curves for pets because we could not control e.g., how many pets households have, as well the pets' price. Finally, we did not find papers which show analyses the influence of pet on consumers' real income.
This scoping review indicated the lack of economic studies which look at the pet consumption via lens of the economic consumption theory and modeling approach. As stated in the introduction pet goods market has been growing steadily for many years and is the prospective one. So, our analysis confirmed that economists are not interesting in more advanced analysis of pet consumption, while pets have been gaining attention among researchers in the field of marketing, psychology and sociology. The next question is: Why not in the economic field?

Conclusions
This scoping review reveals a gap in the pet goods consumption field. We included all found studies in selected databases according to the certain rule of searching, only written in English. Based on our scope review pet goods consumption has not been analyzed so far in the way which allow to answer all questions from the economic perspective even all studies included in review presented in this paper were related to expenses on pet goods. Moreover, no advanced studies regarding pet goods consumption with references to economics topics as e.g., preferences and utility can be found either. This gap may occur due to the fact that pet goods consumption has not been treated in line with the other key economic issues such as households' savings (microeconomics) or global growth (macroeconomics). Furthermore, the lack of standardized methodology of such analysis, well accepted in economic literature may have impacted this gap. But pets consumption have hardly been touched in any formal analysis, economics or otherwise.
However, the review has its limitations, the aim of the paper has been fulfilled. The results of scope review present new directions and findings that could be found in the literature concerning pet goods consumption, especially expenses on pet goods and pet owner economic choices.
Pets become a new family members and should be analyzed in the household economics field like analysis focusing on other household members. The modern lifestyle (putting of maternity, flexible working hours, and getting married latter) fosters household animals into society. Moreover, pets are set to grow in popularity due to COVID-19 (Oliva and Johnston 2021;Giansanti et al. 2022) and it also creates opportunities and hopefully more attention of economists to contribute with their theories to evaluate the impact of this type of the consumption.

Appendices
Appendix A "Pet goods consumption" Search terms for Electronic databases.