Conceptualizing and measuring change
First thing to decide: Qualitative or Quantitative?
If quantitative, for change description purpose: raw gain (difference, change score, raw change), residual gain (linear regression) or percentage. For analysis purpose, the choice of measurement is not a simple issue, and may depend on the theoretical justification for using a change measure, the reliability of change measures as compared with the reliability of measurement of the variables from which the change measures are derived, and the presumed specification of the relationship among the variables in the model.
