In the wake of the Human Genome and HapMap Projects, large amounts of human genetic data have become available. A major proportion of subsequent studies focus on single nucleotide polymorphisms (SNPs). Case-control association studies are particularly popular as they allow for detection of non-random association between an allele and a disease/trait and hence, can be powerful tools for gene mapping.
The proper use of association studies to identify disease-related genes is a topic of active research, especially in terms of the choice of the sample size. Inadequate sample size results in studies that are not statistically powerful and can produce misleading results and is a waste of resources. Thus, it is of utmost importance that sample sizes are carefully calculated before embarking on any study.
OSSE, the Bioinformatics Institute’s Online Sample Size Estimator, provides a convenient way to estimate sample size for case-control association studies. The base values are set for the conventionally used significance level of 5% at 80% power, with minor allele frequencies of 15% and 7% in cases and controls, respectively. This estimates the necessary sample size in the setting of a pilot study, with unknown actual minor allele frequencies.
If prior studies have already provided reliable minor allele frequencies, he user needs to provide minor allele frequencies (in cases and controls), as well as specify the significance level and power he wishes to attain. Case: control ratios diverging from 1:1, quite commonly encountered for rare diseases, can be specified.
Alternatively, the user may choose to calculate significance level or power instead by providing the other variables.
Sample Size Calculator