2x2 factorial design: two trials for the price of one
Published:
Just reminding myself why 2x2 factorial designs give “two trials for the price of one.”
Posts
2025
2024
Power calculations for 1-way ANOVA with possibly unequal group sizes
Published:
I was recently asked to do sample size and power calculations in the setting of a 1-way ANOVA with unequal group sizes. There are solutions to do this when the group sizes are equal, but the answer is not as commonly available for the case where group sizes are unequal.
2023
Power calculations for population attributable fraction (PAF)
Published:
A collaborator recently asked me to do power calculations for the population attributable fraction (PAF) of a dichotomous exposure, $F$, for an incident outcome, $D$. In a previous iteration, we had focused instead on using standard sample size and power calcuation approaches to get a minimum detectable relative risk (RR) assuming known sample size, outcome rate, exposure prevalence, and 80% power. While there is a paper by Browner and Newman (1989) for sample size and power for the PAF, I think an alternate approach could use the minimum detectable RR that I had already computed and the relationship between the PAF and RR.
AUC and AUPRC for non-informative or “no-skill” risk score
Published:
Doing some math to show that the area under the receiver-operating characteristic curve (AUROC or AUC) for a non-informative or “no-skill” risk score or classifier (e.g., coin flip) is 0.5, and the area under the precision-recall curve (AUPRC) is the outcome prevalence.