Tag Archives: Sample size

PMean: Sample size for a study of reproducibility

Dear Professor Mean: I am using a risk stratification tool for patients presenting to the ED with chest pain. This has been a well validated tool in the ED, but I want to show that the scores are reproducible irrespective of the grade of doctor or assessment nurse calculating the score. I’m going to collect a convenience sample of patients presenting to the ED, and after I get informed consent, I will have those patients assessed separately by a triage-trained nurse, an intern doctor, a registrar and a consultant. I will calculation agreement using the intraclass correlation coefficient (ICC). My question is: How do I calculate the sample size in this context? Continue reading

Pmean: The IRB questions my sample size calculation

I got a question today from someone submitting a research protocol to the Institutional Review Board (IRB). The IRB had some concerns about the power calculation. In particular, they said “The IRB would like to know, how you set the parameters for the power calculation, such as effect size, alpha level. For effect size, you need to have some data to justify or should choose a conservative one.”

Part of this was due to an error in the submission of the protocol. We had specified a paired t-test rather than an independent samples t-test, which is a major gaffe on my part. But they were pushing into some tricky territory and I wanted to clear things up. Here is the response that I suggested that we share with the IRB. Continue reading