What is a stepped wedge design?
The stepped-wedge design involves the collection of observations during a baseline period in which no clusters are exposed to the intervention. Following this, at regular intervals, or steps, a cluster (or group of clusters) is randomized to receive the intervention and all participants are once again measured.
What is a non randomized stepped wedge design?
Typically, all units start out untreated, and randomly chosen units switch to intervention at sequential time points until all receive intervention. As randomization is not always feasible, non-randomized stepped-wedge (NR-SW) designs (units switching to intervention are not randomly chosen) have attracted researchers.
Why cluster RCT?
Cluster-randomised controlled trials are used when there is a strong reason for randomising treatment and control groups over randomising participants.
What is the randomization method?
Randomization is the process of assigning participants to treatment and control groups, assuming that each participant has an equal chance of being assigned to any group. 12. Randomization has evolved into a fundamental aspect of scientific research methodology.
What is unit of randomization?
The unit of randomisation is defined statistically as the “who” or “what” that is randomly allocated to treatment. Therefore, in the trial above the unit of randomisation was the episode of acute asthma (answer b).
What are the types of randomization?
The common types of randomization include (1) simple, (2) block, (3) stratified and (4) unequal randomization. Some other methods such as biased coin, minimization and response-adaptive methods may be applied for specific purposes.
How does RCT reduce bias?
By definition, treatment strategies are randomly assigned in RCTs but not in observational studies. Randomization, which prevents bias due to non-comparability between groups, is exploited in full when the data analysis follows the “intention-to-treat” principle.
What is the difference between block randomization and stratified randomization?
After all participants have been identified and assigned into blocks, simple randomization occurs within each block to assign participants to one of the groups. The stratified randomization method controls for the possible influence of covariates that would jeopardize the conclusions of the clinical trial.
The term “stepped wedge” was coined by The Gambia Hepatitis Intervention Study due to the stepped-wedge shape that is apparent from a schematic illustration of the design. The crossover is in one direction, typically from control to intervention, with the intervention not removed once implemented.
What is a stepped wedge cluster randomised trial?
The stepped wedge cluster randomised trial is a novel research study design that is increasingly being used in the evaluation of service delivery type interventions. The design involves random and sequential crossover of clusters from control to intervention until all clusters are exposed.
Is stepped wedge research suitable for evaluation of service delivery interventions?
While not exclusively for the evaluation of service delivery interventions, it is particularly suited to evaluations that do not rely on individual patient recruitment. As in all cluster trials, stepped wedge trials with individual recruitment and without concealment of allocation (or blinding of the intervention) are at risk of selection biases.
Are stepped wedge trials at risk of selection bias?
As in all cluster trials, stepped wedge trials with individual recruitment and without concealment of allocation (or blinding of the intervention) are at risk of selection biases. In a stepped wedge design more clusters are exposed to the intervention towards the end of the study than in its early stages.