This paper attempts to show in a non-mathematical way the influence of grouping on standard deviations and correlations, and advances empirical evidence to illustrate with what accuracy values corrected for grouping by Sheppard's correction approximate to values obtained from ungrouped data when the distributions are continuous. This enquiry gained its initial stimulus from the observation that many standard deviations and correlations reported by students of psychology and education are uncorrected for grouping and that frequently errors attributable to the grouping of data are not small when compared with errors of sampling.