This document contains revised standards for the review of research studies in which individuals are grouped within clusters. They have been developed by the WWC in consultation with experts and will be implemented once they become part of a new WWC Handbook, planned for 2017.

What is the purpose of the WWC Handbook?

The WWC Procedures and Standards Handbook provides a detailed description of the standards and procedures of the WWC. Version 3.0 of the Handbook contains the standards currently in use by the WWC for reviewing studies, including the existing cluster design standards.

How does the WWC review studies that use a cluster design under version 3.0 of the WWC Handbook?

Version 3.0 of the WWC Handbook (pp. 10, 14, 16) and this reviewer guidance document (pp. 5–6) provide a summary of how the WWC uses the current (version 3.0) standards to review cluster studies.

Why is there a new version of the cluster design standards?

The WWC continues to refine its processes, develop new standards, and create new products. In order to ensure that the WWC is appropriately characterizing the evidence from studies that use cluster designs, the WWC revisited the standards in collaboration with a team of evaluation experts. The new cluster standards are intended to improve on the existing cluster design standards in version 3.0 of the Handbook.

How are the revised cluster standards different from the existing standards?

There are several substantive changes to the cluster standards from version 3.0:

1. For studies with cluster designs, the WWC will first review the evidence of an intervention’s direct effect on individual-level (e.g., student) outcomes. If that evidence does not meet standards, the WWC will review the evidence of an intervention’s effect on cluster-level outcomes. The language that study authors use to describe their inferences will have no bearing on the review process.

2. Cluster randomized controlled trials with joiners (individuals who entered clusters after random assignment) may be eligible for the highest rating based on a review protocol specification.

3. Studies that are only able to provide credible evidence of program effectiveness for cluster-level outcomes will no longer be able to receive the highest evidence rating and will be required to demonstrate that the individual-level data used to estimate impacts is representative of the population in the clusters.

When will the revised cluster design standards become part of the WWC Handbook and used by the WWC to review studies?

The revised cluster design standards will replace the cluster design standards in the next release of the WWC Handbook, planned for later in calendar year 2016. The WWC has shared the new standards as a preview of this new version. The revised standards will not be used by the WWC to review studies until the new version of the WWC Handbook is released.

What if I have questions or comments about the cluster design standards?

Readers who have questions or comments about the cluster design standards or the WWC more generally may contact the WWC Help Desk.