Clinical study design is the formulation of trials and experiments in medical and epidemiological research. Many of the considerations here are shared under the more general topic of design of experiments but there can be others, in particular related to patient confidentiality and ethics.
Interrupted time series design (measures on a sample or a series of samples from the same population are obtained several times before and after a manipulated event or a naturally occurring event) - considered a type of quasi-experiment
When choosing a study design, many factors must be taken into account. Different types of studies are subject to different types of bias. For example, recall bias is likely to occur in cross-sectional or case-control studies where subjects are asked to recall exposure to risk factors. Subjects with the relevant condition (e.g. breast cancer) may be more likely to recall the relevant exposures that they had undergone (e.g. hormone replacement therapy) than subjects who don't have the condition.
The ecological fallacy may occur when conclusions about individuals are drawn from analyses conducted on grouped data. The nature of this type of analysis tends to overestimate the degree of association between variables.
Conducting studies in seasonal indications (such as allergies, Seasonal Affective Disorder, influenza, and others) can complicate a trial as patients must be enrolled quickly. Additionally, seasonal variations and weather patterns can affect a seasonal study.
The term retrospective study is sometimes used as another term for a case-control study. This use of the term "retrospective study" is misleading, however, and should be avoided because other research designs besides case-control studies are also retrospective in orientation.
Superiority trials are designed to demonstrate that one treatment is more effective than another.
Non-inferiority trials are designed to demonstrate that a treatment is at least not appreciably worse than another.
Equivalence trials are designed to demonstrate that one treatment is as effective as another.
When using "parallel groups", each patient receives one treatment; in a "crossover study", each patient receives several treatments.