Learn in the textbookDescriptive Statistics (Measures of Central Tendency and Dispersion)
DefinitionA deviation value (偏差値) is a number that shows position within a group on a scale where the mean is 50 and each standard deviation is worth 10.
ExplanationAs a formula, deviation value = 50 + 10 × (value − mean) ÷ standard deviation. A value exactly at the mean scores 50, one standard deviation above scores 60, and one below scores 40. Tests with different maximum scores or difficulty can thus be compared on the same scale.
AnalogyLike exchanging different national currencies into one currency before comparing, it converts each group's scores onto a common scale before comparing them.