Best number of genes (<i>N</i>) used in age estimation and the difference of median of age is the absolute difference between the median of estimated age and the median of chronological age.

<p>The significance of the error was determined by obtaining 1,000 randomized cross-validation errors with age information randomly shuffled; the significance of the prediction error is the fraction of the 1,000 randomized errors lower than the actual cross-validation error. The best <i>N</i> varies across regions.