Results Summary

What was the project about?

In a stepped-wedge cluster randomized trial, or SW-CRT, researchers compare new treatments to standard treatments in groups of patients, such as patients at different clinics, to look at the treatments’ effectiveness. They assign groups by chance to switch from the standard to new treatment at different time points until all groups have received the new treatment. The different time points to switch treatments are called steps.

SW-CRTs take time and resources. If researchers know they can’t collect data on all groups and all steps in a SW-CRT, they can plan to use an incomplete SW-CRT design. In incomplete SW-CRTs, researchers plan the study knowing that some clinics or steps will have missing data. But researchers need better guidance for planning incomplete SW-CRTs that still get accurate results.

Also, current methods for planning how many patients and groups should take part in SW-CRTs don’t work well for large studies. They also don’t work well with certain types of outcomes, like yes or no outcomes; outcomes that have counts, like number of hospital visits; or continuous outcomes, like a score from 0 to 100.

In this study, the research team developed and tested new methods to design and analyze SW-CRTs with different patterns of planned missing data, large data sets, and different types of outcomes.

What did the research team do?

First, the research team created new methods to identify which data could be missing while still getting accurate results. The team used data from real SW-CRTs. They looked at many scenarios to find the number of patients and clinics needed. For each scenario, the team left out data for different types of outcomes, including yes or no, count, and continuous outcomes.

Next, the research team developed new methods to analyze SW-CRTs with large numbers of patients. They combined data in each group at each step to see the effect of the planned missing data on the study results.

The research team created computer programs to help other researchers use the new methods.

What were the results?

The new methods correctly measured the effect of planned missing data on study results in incomplete SW-CRTs. With this information, the research team was able to find the best way to design and analyze incomplete SW-CRTs with large data sets and different types of outcomes.

What were the limits of the project?

The research team tested the methods with SW-CRTs that group patients at a single level, such as by clinic. The study didn’t test the methods for SW-CRTs that group patients at more than one level, such as by doctors within clinics.

Future research could apply the methods to SW-CRTs that group patients at more than one level.

How can people use the results?

Researchers can use these results to design and analyze SW-CRTs.

Final Research Report

This project's final research report is expected to be available by November 2024.

Peer-Review Summary

Peer review of PCORI-funded research helps make sure the report presents complete, balanced, and useful information about the research. It also assesses how the project addressed PCORI’s Methodology Standards. During peer review, experts read a draft report of the research and provide comments about the report. These experts may include a scientist focused on the research topic, a specialist in research methods, a patient or caregiver, and a healthcare professional. These reviewers cannot have conflicts of interest with the study.

The peer reviewers point out where the draft report may need revision. For example, they may suggest ways to improve descriptions of the conduct of the study or to clarify the connection between results and conclusions. Sometimes, awardees revise their draft reports twice or more to address all of the reviewers’ comments.

Peer reviewers commented and the researchers made changes or provided responses. Those comments and responses included the following:

  • The reviewers lauded the researchers for preparing an informative and well-written final report.
  • The primary change the reviewers requested in this highly statistical report was for the researchers to add summary text in each section to explain the information in that section in plain language. The researchers made these additions.

Conflict of Interest Disclosures

Project Information

John S. Preisser, PhD
University of North Carolina at Chapel Hill
Incomplete Stepped Wedge Designs: Methods for Study Planning and Analysis

Key Dates

November 2019
October 2023

Study Registration Information


Has Results
Award Type
State State The state where the project originates, or where the primary institution or organization is located. View Glossary
Last updated: March 14, 2024