Comparing Rating Scales of Different Lengths: Equivalence of Scores from 5-Point and 7-Point Scales

Using a self-administered questionnaire, 227 respondents rated service elements associated with a restaurant, retail store, or public transport company on several 5-point and 7-point rating scales. Least-squares regression showed that linear equations for estimating 7-point from 5-point and 5-point from 7-point ratings explained over 85% of the variance and fitted the data almost as well as higher-order polynomials and power functions. In a cross-validation on a new data set the proportion of variance explained fell to about 76%. Functionally inverse versions of the derived linear equations were calculated for the convenience of researchers and psychometricians.