What is a Q-Q plot?
The Q-Q (Quantile-Quantile) plot provides a visual comparison of two populations and is a plot of the sampled t-statistic vs. a theoretical t-statistic. The Q-Q plot can indicate the degree a sample diverges from a normal distribution. Points which deviate markedly from a linear relationship to a theoretical t-statistic could be considered suspect genes exhibiting differentially expression. The Q-Q plots allow you to visualize the magnitude of differentially gene expression within the sample tested based on the Students t-test. However, the ordinary Student t-test is not ideally suited for microarray data because a large t-statistic can be driven by an unrealistically small standard deviation. The Q-Q plots are produced using the R statistical language with the Bioconductor package.
