October 1, 2018: Dr. Greg Simon Uses a Pie Eating Contest Analogy to Explain the Intraclass Correlation Coefficient

In a new video, Dr. Greg Simon explains the intraclass correlation coefficient (ICC) with an analogy to a pie eating contest. The ICC is a descriptive statistic that measures the correlations among members of a group, and it is an important tool for cluster-randomized pragmatic trials because this calculation helps determine the sample size needed to detect an effect.

Greg Simon from NIH Collaboratory on Vimeo.

“When we randomize treatments by doctors, clinics, or even whole health systems, we need to think about how things cluster, and the intraclass correlation coefficient is the measure of that clustering. When we think about sample sizes in pragmatic clinical trials, it’s important to understand what an intraclass correlation coefficient actually is.”

For most pragmatic trials, the ICC will be between 0 and 1. If the outcomes in a group are completely correlated (ICC=1), then all participants within the group are likely to have the same outcome. When ICC=1, sampling one participant from the cluster is as informative as sampling the whole cluster, and many clusters will be needed to detect an effect. If there is no correlation among members of the groups (ICC=0), then the available sample size for the study is essentially the number of participants.

For more on the ICC, see the Intraclass Correlation section in the Living Textbook or this working document from the Collaboratory’s Biostatistics and Study Design Core.

December 7, 2017: Dr. Greg Simon Explains Individual, Cluster, and Stepped-Wedge Randomization in a New Prop Video

In a new video in the Living Textbook, Dr. Greg Simon describes the differences between individual, cluster, and stepped-wedge randomization using props, including marbles, Play-Doh, and glassware.

“In the end, it’s all about randomly assigning who gets which treatment, or who gets which treatment when, so that we’re able to make some un-biased judgement about which treatment is really better.” —Greg Simon, MD

New Biostatistical Guidance Document Available: Small-Sample Robust Variance Correction for GEE

Tools for ResearchThe NIH Collaboratory’s Biostatistics and Study Design Core has just published a new guidance document by Andrea Cook, PhD, of the Group Health Research Institute, on using small-sample robust variance correction for generalized estimating equations (GEE) for use in cluster-randomized trials. The document, which includes guidance on methods available in the SAS and Stata statistical analysis packages, is available directly from the NIH Collaboratory Knowledge Repository here (opens as PDF), or via the Biostatistical Guidance Documents page in the Living Textbook.

This guidance document is one in a series of research tools focused on detailed aspects of statistical design for conducting pragmatic clinical trials. Each document in this series provides a synthesis of current developments, discusses possible future directions, and, where appropriate, makes recommendations for application to pragmatic clinical research.


New Biostatistical Guidance Document Available – “Frailty Models in Cluster-Randomized Trials”


Tools for ResearchThe NIH Collaboratory Biostatistics/Study Design Core has released a new guidance document concerning the use of frailty models in the setting of cluster-randomized trials (CRTs). This guidance, the fifth in a series from the Core, outlines considerations affecting power calculations in frailty models, as well as issues raised by the use of logistic regression models for time-to-event versus dichotomous outcomes in CRTs .

The guidance document can be found under Biostatistical Guidance Documents on the Tools for Research page on the Living Textbook, or accessed directly here (PDF).


Collaboratory Biostatistics and Study Design Core Releases Guidance Documents


The NIH Collaboratory’s Biostatistics and Study Design Core has released the first in a series of guidance documents focusing on statistical design issues for pragmatic clinical trials. Each of the four guidance documents are intended to help researchers by providing a synthesis of current developments in the field, discuss possible future directions, and, where appropriate, make recommendations for application to pragmatic clinical research.

The guidance documents are available through the Living Textbook and can be accessed on the “Tools for Research” tab or directly here.