The magnitude of the effect of smaller family sizes on the increase in the prevalence of asthma and hay fever in the United Kingdom and New Zealand☆,☆☆,★
Section snippets
METHODS
Data on family size for England/Wales and New Zealand was obtained from the Office of Population Censuses and Surveys19 and Statistics New Zealand,20, 21 respectively, for the period 1961 to 1991. For the United Kingdom data were available for the birth order of children, expressed as a percentage of children. For New Zealand data were available for the number of children per family, expressed as a percentage, based on all families with children. The relative change in family size over the
RESULTS
The studies included in the analysis are shown in Table I.
Study Country Study design Population (y) Sample size Outcome measure Leadbitter et al33 New Zealand Cohort 13 734 Asthma ever Wickens et al34 New Zealand Case-control 7-9 233 cases/241 controls Diagnosed asthma and current medication use Shaw et al35 New Zealand Cross-sectional 8-13 708 Current wheeze Moyes et al32 New Zealand Cross-sectional 6-7 2,614 Diagnosed asthma Lewis et al36 England, Scotland, and Wales Cohort 16
DISCUSSION
Although most studies show an increase in asthma and hay fever prevalence over time, estimating the relative size of this increase between the years 1961 and 1991 (when government statistics were available on family size) is difficult because of the different dates at which point prevalences are reported. For example, no studies were located that reported asthma symptom or hay fever prevalence at 1961 and at 1991. However, a Scottish study1 reported an increase in wheeze prevalence from 10.4%
Acknowledgements
We thank Dr Christopher D. Moyes for providing us with more detailed data than was reported in his publication.32
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Supported by a Programme Grant from the Health Research Council of New Zealand.
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Reprint requests: Kristin Wickens, DPH, Wellington Asthma Research Group, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand.
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0091-6749/99 $8.00 + 0 1/1/99998