# Can I use difference score as DV and use the baseline score as IV?

Can I use a difference score as the dependent variable and use the baseline score as the independent variable when doing correlation, linear regression and multivariate linear regression? Thank you.

• Are you asking whether you can use the baseline score to predict the difference in scores? I don't know what type of data and domain you're working with -- but just based on the information you've provided in the question, I don't see any problems in doing this. Apr 5, 2016 at 19:39
• Thank you. yes , I would like to use the baseline score to predict the difference in score. The score is continuous data. actually I am using the functional level score for my patient to predict the improvement of their functional score in the hospital. Apr 6, 2016 at 16:57

If the variables are measured less than perfectly, this is a bad idea because you will be predicting the error of the baseline measure. E.g. suppose person 1 had a "good day" at BL and person B had a "bad day". Then, even if neither changes, it will look like they did.

You should use a multilevel model.

• thank you, yes you are right What do you mean by multilevel model?? Apr 6, 2016 at 16:58
• A multilevel model is one way of analyzing data that is not independent. Apr 6, 2016 at 19:12
• @PeterFlom, but isn't that true for all regression models? We assume that error in measurement is present only in the $y$ but ignore the error in measurement for all $x$'s? Apr 6, 2016 at 19:50
• Not to the same extent. Apr 6, 2016 at 22:10
• Should I still run the multivariate linear regression using the baseline score and other independent that are significant predictors? Apr 9, 2016 at 18:22

Given you have the same thing measured twice you could either do

lm(y2 ~ y1 + x, data = df)


or treat it as multilevel/repeated measures to account for the nesting of the two occasions within subjects as @Peter Flom noted)

m1 = nlme::lme(y ~ x, random = ~ 1|SID, data = df)