Asthma prevalence and deprivation: a small area analysis

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Abstract
STUDY OBJECTIVE: To investigate the relation between the prevalence of asthma symptoms in adults and deprivation in the area of residence. DESIGN: Two complementary surveys carried out between 1991-1993 yielding adult asthma symptom prevalence throughout New Zealand. Deprivation is measured by the NZDep91 index of deprivation for small areas. SETTING: New Zealand. PARTICIPANTS: A random sample of 25,042 adults aged 20-50 years. MAIN RESULTS: After controlling for possible confounding by age, gender, and ethnicity, the 12 month period prevalence rates of asthma in this representative sample of New Zealand adults are significantly higher in the three most deprived area categories than in the least deprived (tenth) category. The prevalence ratio for the most deprived category compared with the least deprived category is 1.29 with 95% confidence intervals (CI) 1.14, 1.47. There is a linear increase in asthma prevalence with increasing area deprivation (chi 2(1) = 32.20, p < 0.001). Independently, the rates are also 1.41 (95% CI 1.29, 1.54) times higher among Maori and 1.29 (95% CI 1.10, 1.52) times higher among the Pacific Island group than among the remaining, mostly European, respondents. CONCLUSIONS: The relation between asthma in adults and area deprivation is unlikely to be attributable to study biases or confounding. Further work should examine the possible role of modifiable deprivation factors in this relation.