Methods at a Glance
This section provides information and examples of methodological issues to be aware of when working with different study designs. Virtually all studies face methodological issues regarding the selection of the primary outcome(s), sample size estimation, missing outcomes, and multiple comparisons. Randomized studies face additional challenges related to the method for randomization. Other studies face specific challenges associated with their study design such as those that arise in effectiveness-implementation research; multiphase optimization strategy (MOST) studies; sequential, multiple assignment, randomized trials (SMART); crossover designs; non-inferiority trials; regression discontinuity designs; and paired availability designs. Some face issues involving exact tests, adherence to behavioral interventions, noncompliance in encouragement designs, evaluation of risk prediction models, or evaluation of surrogate endpoints.
Experiments, including clinical trials, differ considerably in the methods used to assign participants to study conditions (or study arms) and to deliver interventions to those participants.
This section provides information related to the design and analysis of experiments in which (1) participants are assigned in groups (or clusters) and individual observations are analyzed to evaluate the effect of the intervention, (2) participants are assigned individually but receive at least some of their intervention with other participants or through an intervention agent shared with other participants, and (3) participants are assigned in groups (or clusters) but groups cross-over to the intervention condition at pre-determined time points in sequential, staggered fashion until all groups receive the intervention.
This material is relevant for both human and animal studies as well as basic and applied research. And while it is important for investigators to become familiar with the issues presented on this website, it is even more important that they collaborate with a methodologist who is familiar with these issues.
In a parallel group-randomized trial, also called a parallel cluster-randomized trial, groups or clusters are randomized to study conditions, and observations are taken on the members of those groups with no crossover of groups or clusters to a different condition or study arm during the trial.
In an individually randomized group-treatment trial, also called a partially clustered design, individuals are randomized to study conditions but receive at least some of their intervention with other participants or through an intervention agent shared with other participants.
In a stepped wedge group-randomized trial, also called a stepped wedge cluster-randomized trial, groups or clusters are randomized to treatment sequences which cross-over to the intervention condition at predetermined time points in a sequential, staggered fashion until all groups receive the intervention.
NIH Clinical Trial Requirements
The NIH launched a series of initiatives to enhance the accountability and transparency of clinical research. These initiatives target key points along the entire clinical trial lifecycle, from concept to reporting the results.