Assumption of Equal Intervals – Calculations on Ordinal Variables

The assumption of equal intervals says that all distances between adjacent answer categories are equal in the repondents’ perception. This assumption is an attempt to justify treating ordinal variables as if they were metric variables. Doing so enables one to compute means, standard deviations and Pearson correlations on ordinal variables. This is simpler than using more appropriate techniques. Assumption of Equal […]

How to Mean Center Predictors in SPSS?

For testing moderation effects in multiple regression, we start off with mean centering our predictors:mean centering a variable is subtracting its mean from each individual score.After doing so, a variable will have a mean of exactly zero but is not affected otherwise: its standard deviation, skewness, distributional shape and everything else all stays the same. After mean […]