What is a good intracluster correlation coefficient?
Values of ρ range from 0 to 1 in human studies. A very small value for ρ implies that the within-cluster variance is much greater than the between-cluster variance, and a ρ of 0 shows that there is no correlation of responses within a cluster. Usually, values of r are between 0.01 and 0.02 in human studies.
How do you read design effects?
The design effect is the ratio of the actual variance to the variance expected with SRS. It can more simply be stated as the actual sample size divided by the effective sample size (the effective sample size is what you would expect if you were using SRS). For example, let’s say you were using cluster sampling.
How is the intracluster correlation coefficient ( ICC ) used?
The intracluster correlation coefficient (ICC),or ρ (the Greek rho), is a measure of the relatedness of clustered data. It accounts for the relatedness of clustered data by comparing the variance within clusters with the variance between clusters.
Why do we use confidence intervals in ICC?
Confidence intervals were suggested as the primary mechanism for providing information on the precision of the ICC, but the number of clusters together with the average cluster size and the range of cluster sizes (or some other measure of spread) were also put forward as appropriate descriptors.
Why is the ICC important in cluster trials?
To aid the interpretation of the results of cluster trials, it is important that appropriate information is presented in their reports. The ICC for each trial outcome is widely acknowledged to be one of the primary factors which helps researchers interpret the results of the trial.
How are ICCS used to interpret trial results?
The ICC for each trial outcome is widely acknowledged to be one of the primary factors which helps researchers interpret the results of the trial. It also helps researchers planning new trials in the area, as estimates of ICCs are used to inform sample size calculations – standard sample size calculations require to be inflated by a factor: