Dear Professor Mean, I would like to conduct a meta-analysis of several studies. The data in these studies were evaluated using an ordinal scoring system coded as 0,1,2,3. How to I combine the results of these studies? Continue reading
Category Archives: Statistics
PMean: I need a clinical research coordinator
Dear Professor Mean, I run a clinic and have a company interested in having my patients participate in a clinical trial. They tell me that I need to have a clinical research coordinator. What is that, exactly, and how much would it cost? Continue reading
PMean: Cox regression in R
I wanted to show a couple of Cox proportional hazards regression models in R for a talk I am giving for the R users group. Continue reading
PMean: More Kaplan-Meier curves in R
I found a larger data set and wanted to show how you could use the Kaplan Meier curves as a preliminary screen of some categorical and continuous variables in a larger and more complex data set. Continue reading
PMean: Kaplan-Meier curves in R
I am giving a talk about using R for survival analysis and I wanted to talk first about the Kaplan-Meier curve and how you might draw it in R. Continue reading
Recommended: Sample size of 12 per group rule of thumb for a pilot study
This study is (sadly) not available for free on the Internet, but it is still worth highlighting here. Steven Julious provides some justification for the use of twelve patients per group in a pilot study. This is a useful starting point for discussion, and it may serve as a useful lower bound. I would suggest that you consider the size of the larger trial that you are piloting. For a larger study that might require thousands or tens of thousands of patients, a pilot study of 12 patients per group is woefully inadequate. Continue reading
PMean: What is the probability of a probability of one
Someone wrote asking me about a variation of the “Rule of Three”. This rule says that if you observe zero events out of n, an upper 95% confidence limit for n is approximately 3/n. So suppose you operated on 10 patients and none of them died after surgery. Then you would be 95% confident that the mortality rate would be 30% (3/10) or less. This person asked “Suppose I repeatedly sample from a population and every patient in the sample was a G. What is the how likely is it that the entire population is Gs?” This flips the problem around, and is equivalent to saying that the probability of survival is 97% or greater. But this person wanted an estimate of the probability that the probability in the population is 1. Continue reading
PMean: An example of a simple sample size justification
Someone asked me for a sample size justification for a study involving a historical control group of 30 patients and a treatment group of unspecified size. I thought it would be nice to document the mechanics of this calculation here, as an example for future clients. It uses a program, Piface, developed by Russ Lenth for sample size calculations. Continue reading
PMean: A brief abstract of my research interests
I attended a working group meeting for researchers interested in Chem bio Defense applications. They asked each attendee to write a brief abstract of their research interests and expertise to share with the others. This will help in identifying areas of possible collaboration. Here is what I wrote: Continue reading
PMean: Simple longitudinal data sets to illustrate data management
I am working on a class that will teach basic data management and graphics using the R programming language with parallel classes in SPSS and SAS. On the third or fourth day of the class, we will look at managing longitudinal data sets, as these require special skills. I wanted to find a couple of reasonably simple longitudinal data sets that were available on the web and which had at least a few missing values in them. Here’s a couple of data sets that might work. Continue reading