Median Split

Splitting a continuous variable into two groups at its median is sometimes used in data analysis. On average, splitting a predictor variable is equivalent in correlation and regression to replacing all the values with either the mean value for the low group or the high group, as appropriate. Each data value is replaced by the weighted average , where is the mean for the group containing and is a weight value with . Moving the weight slider to the right moves the values toward a median split. Observe the decrease in , the -statistic, its -value, and the predictor's variance as the data is moved towards the equivalent of a median split. Much is lost and nothing gained by a median split.