APA Dictionary of Psychology

a procedure for converting a set of data in which each value, x_i, is replaced by its square root, another number that when multiplied by itself yields x_i. Square-root transformations often result in homogeneity of variance for the different levels of the independent variable (x) under consideration. As with transformations generally, the goal is to obtain data that more closely meet the assumptions of a statistical procedure that is to be applied.