Throughout our lives, we are exposed to many factors that can affect our health and wellbeing. But what kinds of factors influence specific health outcomes? And what do we do when we become ill? Health researchers dedicate their working lives to answering a huge range of different clinical research questions and they do so by carrying out very specific studies. The findings from these studies eventually lead to the development of interventions that can help save lives.
Flowchart adapted from: Grimes, D. A., & Schulz, K. F. (2002). “An overview of clinical research: The lay of the land”. The Lancet, 359(9300), 57-61
In clinical research, a study design is a plan for selecting study subjects and for obtaining data. These study designs fall into two different categories:
These categories are based on whether or not the investigators assign a particular exposure to a cohort.
Investigators assign exposures (for example, a trial to test the effectiveness of a new medication) and these are categorised into randomized (studies with a control, or comparison, group) and non-randomized trials (those without a control group).
These studies focus on exposures that are already present in a population and assess the effects of the exposure on that cohort. These studies are further categorised into analytical and descriptive.
Not all study types will be appropriate for answering a particular clinical question. For example, if you wanted to investigate the impact of maternal smoking on foetal development, then a randomized-controlled trial would not be appropriate as it is not ethical to assign a disease or potentially harmful exposure to an individual. In this case, an observational study would be more appropriate.
This table illustrates the most appropriate study designs for answering specific types of clinical questions.
|Clinical Question||Appropriate Study Design|
|Does this treatment work? (Intervention)||
|How good is a diagnostic test? (Diagnosis)||
|Should we screen? (Screening intervention)||
|What factors contribute to this disease? (Aetiology)||
|How does this disease develop? (Prognosis)||
In this learning series, we will examine each study design type in more detail, the types of clinical questions they investigate and the methodologies applied in each study design.