*Geek Box: Longitudinal Study
‘Longitudinal’ in research design simply means ‘over time’. Longitudinal studies are observational, and data is collected on the same group of participants repeatedly on the same measures over a period of time. Technically, the timeframe could be as short as a week or as long as decades. Given their observational nature, they are used primarily to look at the associations between an exposure and an outcome. The exposure may be an intervention – diet, drug, or otherwise – and the outcome may be risk factors for a disease, or overt disease itself.