A Multilevel Analysis of Socioeconomic (Small Area) Differences in Household Food Purchasing Behaviours

Study objective: To examine the association between area- and individual-level socioeconomic status (SES) and food purchasing behaviour. Design: The sample comprised 1000 households and 50 small areas, selected using a stratified two-stage cluster design. Data were collected by face-to-face interview (66.4% response rate). SES was measured using a composite area index of disadvantage (mean 1026.8, sd=95.2) and household income. Purchasing behaviour was scored as continuous indices ranging from 0 to 100 for three food-types: fruits (mean 50.5, sd=17.8), vegetables (61.8, 15.2), and grocery items (51.4, 17.6), with higher scores indicating purchasing patterns more consistent with dietary guideline recommendations. Setting: Brisbane metropolitan region, Australia, 2000 Participants: Persons aged 16-94 who were primarily responsible for their household’s food purchasing. Main results: Controlling for age, gender, and household income, a two standard deviation increase on the area-based SES measure was associated with a 2.01 unit-increase on the fruit purchasing index (95% CI -0.49 to 4.50). The corresponding associations for vegetables and grocery foods were 0.60 (-1.36 to 2.56) and 0.94 (-1.35 to 3.23). Prior to controlling for household income, significant area-level differences were found for each food, suggesting that clustering of household income within areas (a composition effect) accounted for the food purchasing variability between them. Conclusions: Living in a socioeconomically disadvantaged area was associated with a tendency to have a healthier food purchasing profile, however, the magnitude of the association was weak-to-moderate and the 95% confidence intervals for area-SES included the null. Even though urban areas in Brisbane are differentiated on the basis of their socioeconomic characteristics, it seems unlikely that where you live shapes your procurement of food over and above your personal characteristics. This is in contrast to metropolitan regions of the US and Britain, where spatial segregation along socioeconomic lines is large enough to be detectable in people's food behaviour and dietary intakes.