Table 2 Strengths and weaknesses of asthma cohort studies
Prospective data collection (no recall bias)Can be difficult to change study protocol, e.g. retrospectively add data, change outcome
Hypothesis drivenStill does not prove causation
Essential for intervention studiesRecruitment of representative population
Longitudinal analysis can reduce sample sizeDrop out
Analysis can minimise effect of drop outOften only considers one exposure
Able to consider different exposures at different timesCost
Follow up for >10 years often necessary
Lack of gold standard outcome