Power Calculator for Repeated-Low Dose Challenge Studies

This calculator computes the statistical power of a randomized controlled repeated-low dose challenge study in non-human primates given the inputs provided. Power is for testing the null hypothesis that the relative risk (vaccine group vs control group) of infection per challenge is one versus the alternative hypothesis that the relative risk equals the input value. For a detailed description of the method see:

MG Hudgens, PB Gilbert. Assessing vaccine effects in repeated low-dose challenge experiments. Biometrics, 65(4):1223-1232, 2009.

MG Hudgens, PB Gilbert, JR Mascola, CD Wu, DH Barouch, SG Self. Power to Detect the Effects of HIV Vaccination in Repeated Low-Dose Challenge Experiments. Journal of Infectious Diseases, 200(4):609-613, 2009.


Step I: Select one or more tests you wish to use to evaluate the power

Log Rank

Fisher's Exact

Likelihood Ratio


Step II: Input parameter values and compute power

ParameterInputNotes
Maximum number of challenges per animal (cmax) The maximum number of times each animal will be exposed to the virus.
Per-challenge probability of infection without vaccine (p0)
Relative risk of infection (RR) The relative risk of infection per challenge. Values of RR < 1 indicate the vaccine has a protective effect. For example, RR = 0.4 corresponds to 60% vaccine efficacy (VE) where VE = (1-RR) x 100%.
Immune fraction The fraction of animals that are not susceptible to infection.
Number of animals vaccinated (nv)
Number of control animals (np)
Number of simulations At least 1000 is recommended for final power calculations. Maximum allowed is 10,000.
2-sided alpha The 2-sided type I error rate of the test.