Test for trend: evaluating dose-response effects in association studies

In a prospective cohort study, the association between maternal stress and asthma in children was evaluated. The authors were interested in determining the effect that increasing levels of maternal stress has on the prevalence of asthma in offspring by 6 years of age. Maternal stress was measured using a questionnaire and categorized as 0, 1-2, 3-4, or 5 negative pre-and post-natal life events; asthma was diagnosed by physicians. The authors reported that increasing levels of maternal stress, compared with zero negative events, were associated with increasing odds of offspring having asthma during childhood: for 1-2 events, OR = 1.30 (95% CI: 0.72-2.37); for 3-4 events, OR = 1.92 (95% CI: 1.03-3.57); and for 5 events, OR = 3.52 (95% CI: 1.79-6.93). The p for trend (ptrend) was < 0.01 (Figure