Socioeconomic inequalities in food purchasing: The contribution of respondent-perceived and actual (objectively measured) price and availability of foods
Introduction
Unhealthy dietary intakes are significant contributors to major chronic conditions such as cardiovascular disease and cancer (National Health and Medical Research Council, 2003). These diseases show marked socioeconomic gradients; lower socioeconomic groups experience higher mortality and morbidity rates from cardiovascular disease and some cancers than their more advantaged counterparts (Dalstra et al., 2005, Mackenbach et al., 2000). Unhealthy dietary intakes have been identified as key contributing factors to these health inequalities (Davey Smith and Brunner, 1997, James et al., 1997, Smith and Baghurst, 1992).
Dietary guidelines aim to decrease the burden of disease amongst the general population and socioeconomically disadvantaged groups in particular. The guidelines advocate making food choices that are low in fat, saturated fat, salt and sugar, and higher in dietary fibre (National Health and Medical Research Council, 2003). Lower socioeconomic groups are less likely to make food choices consistent with these recommendations (Turrell et al., 2002, Roos et al., 1996). Much research has focussed on the individual-level determinants of socioeconomic inequalities in diet. This focus has tended to ignore the context in which individuals make decisions about food choice (Cummins and MacIntyre, 2002). Two recent reviews concluded that we know relatively little about how availability and price are associated with intakes (Kamphuis et al., 2006, Giskes et al., 2007). Additionally, we know even less about how these factors influence food purchasing (a behaviour that precedes intakes) and socioeconomic inequalities in food purchasing.
A growing body of evidence has examined the location of supermarkets as a proxy for the availability of a wide variety of foods at low prices. Studies in the US and Canada have found that deprived and minority areas are less serviced by supermarkets, but have more independent grocery stores (that stock a limited range of items at higher prices) (Cummins and Macintyre, 2006). The opposite trend was found for retail provision in the UK; a greater number of supermarkets/discounters were located in deprived areas, and the price and availability of a range of foods did not show much variation by area deprivation (Cummins and MacIntyre, 2002). An Australian study did not find any association between access to food retail outlets (assessed in terms of distance, numbers of local shops and their opening hours) and area deprivation (Winkler et al., 2006a). A number of natural experiment studies in the UK have not shown convincing evidence that increased access to a wide variety of foods at low prices was associated with improvements in residents' dietary behaviours (Cummins et al., 2005). While many of these studies have looked at area-level infrastructure as a proxy for the availability and price of foods, the reality is that some participants may choose to shop in other areas. A potentially more insightful (and arguably more realistic) method of examining the role of availability and price on food purchasing decisions is assessing the availability and price of items in the shops where participants reported doing their shopping. No known study has done this to date.
Research on food retail provision and the availability and price of foods has almost exclusively relied on objectively measured data (e.g. Cummins and MacIntyre, 2002, Winkler et al., 2006b). The use of objective data may only tell part of the story about how availability and price mediate socioeconomic differences in food purchasing. People's food purchasing may also be driven by their perceptions of availability and price, and differential perceptions may contribute to socioeconomic inequalities in food purchasing. A number of studies have shown that lower socioeconomic groups perceive that some recommended foods (i.e. choices lower in fat, saturated fat, sugar, salt or higher in fibre) are not always available where they shop (Kearney and McElhone, 1999, Kearney et al., 2000). Additionally, lower socioeconomic groups are more likely to perceive a recommended diet to be more expensive (Kearney and McElhone, 1999, Giskes et al., 2002). While there has been much work on the objective environment to date, we are not clear about where interventions would be best targeted to bring about dietary change. It is currently unknown which strategy may be most effective in improving population dietary behaviour and decreasing inequalities in these: making changes to the actual food purchasing environment or focussing on people's perceptions of the food environment.
In the current study we examined the relative contribution of perceived and objective price and availability of recommended foods to household income differences in food purchasing. We addressed these aims using objective availability and price data from supermarkets where participants shopped and participant's perceptions of food availability and price in these same stores.
Section snippets
Data collection
Data for this study were collected as part of the 2000 Brisbane Food Study in Brisbane, Australia. Two methods of data collection were employed: (1) a face-to-face structured interview to assess food purchasing behaviour, and obtain the name and address of the supermarket where participants do most of their grocery shopping and participant's perceptions of the availability and price of a range of food items at this supermarket; and (2) supermarket audits to objectively assess the availability
Results
Table 3 shows the objective and perceived availability and price of each of the recommended and regular food choices. There was little variation in the availability of the recommended items in the supermarkets: the recommended choices were stocked by almost all supermarkets. Therefore, objective availability was not used in subsequent analyses to explain variation in food purchasing and socioeconomic inequalities in food purchasing. The recommended choices were more expensive than the regular
Discussion
We found that the actual (objectively measured) price differences between recommended and regular choices and availability of foods were not associated with the purchase of recommended foods and did not contribute to socioeconomic inequalities in food purchasing. Perceived availability and price differences of recommended foods were associated with their purchase; participants that perceived them as available and no more expensive than recommended choices were more likely to purchase them.
Conclusions
The findings of this study suggest that inequalities in the purchase of recommended foods may have little to do with the food shopping environment and may be more a consequence of household or individual-level factors. There is little evidence outside of the US that justifies interventions changing the food shopping infrastructure to decrease socioeconomic inequalities in food choice. The current study showed that targeting perceptions of the environment would be more fruitful for bringing
Acknowledgments
We would like to acknowledge Marie-Andree Roy for her work in developing the price and availability data collection instruments. Dr Katrina Giskes is supported by an Australian National Health and Medical Research Council Sidney Sax International Postdoctoral Fellowship (ID 290540). A/Professor Gavin Turrell is supported by an Australian National Health and Medical Research Council Senior Research Fellowship (ID 390109).
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