It is uncertain whether this represents an increase in incidence or a longer duration of disease. To conclude, retrospective estimates of trends in asthma incidence are likely to be severely biased by differential recall.Ī number of studies of various designs have documented a long-term increase in asthma prevalence in children 1– 5 and to a certain extent in adults 6– 16. There was only a 20% difference in the cumulative incidence of asthma. The prospective study showed the opposite, with an OR of 0.2 comparing those born in 1969 with those born in 1927. The retrospective analysis showed a large increase in asthma incidence by year of birth, with an odds ratio (OR) of 2.9 comparing those born in 1969 with those born in 1927. Analyses of incident asthma in the period 1985–1996 were compared between the studies.
In the retrospective study in 1998, subjects reported the age at which the disease started. In the prospective study, subjects without asthma were followed from 1985–1996/1997. Retrospective and prospective asthma incidence by year of birth were compared in the same community, during the same time period, from two independent studies a cohort study and a cross-sectional study in Western Norway. The validity of this retrospective approach is unknown. Several retrospective studies have shown an increase in asthma incidence by year of birth, consistent with an increasing trend in asthma incidence. There is evidence for an increase in adult asthma prevalence.
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