Statistical Issues for Longevity Studies in Animal Models

This chapter provides an overview of basic statistical concepts and procedures that are germane to researchers interested in aging. In the planning stage of research, the researchers should generate a formal hypothesis or set of hypotheses based on previous research and/or theories that are yet to be formally tested. Sample size calculation is a procedure for calculating the sample size required to achieve a desirable degree of statistical power. The calculation is based upon a selected statistical test, an estimate of the variation in the population, an established significance level, and an expected effect size. Parametric methods, on the other hand, are valid only under certain distributional conditions. Most parametric methods, such as the t-test, require that observations be approximately normally distributed, and both groups should have equal sample variances. The t-test is a parametric statistical method used for testing the difference in a mean from a hypothesized value or the difference in means between two normally distributed populations with equal variances.