Research Measurements
SD
Standard Deviation
A measure of how spread out data values are from the average.
Standard deviation (SD) quantifies the amount of variation or dispersion in a set of data values. A low SD indicates data points cluster closely around the mean, while a high SD indicates wide spread. In supplement research, SD reflects individual variability in response to treatment. For example, an average hair count increase of 20 hairs/cm² with SD of 5 suggests consistent response, while SD of 30 suggests highly variable individual outcomes. SD is essential for calculating confidence intervals, effect sizes (Cohen's d = mean difference / pooled SD), and determining required sample sizes for adequate statistical power.