Hi all, I am doing a matched (1:10) case-control study looking at the association between income (in ranks) and the risk of stroke. I use conditional logistic regression:   PROC LOGISTIC desc data = stroke; strata = matched; model stroke (event = '1') = INCOMErank; RUN; matched = matching variable stroke: 0 = no stroke, 1 = stroke Now I wish to look at potential non-linearity using cubic splines with knots at the 20, 50, 80th percentile of INCOME rank. Moreover, I wish to output the odds ratio for each rank compared to the 50th percentile INCOME rank. My goal is to achieve a figure with odds ratios on the y-axis and income-ranks on the x-axis. How would you do cubic splines with knots in conditional logistic regression?  How do you obtain odds ratios comparing each rank to a reference for a continuous variable? Thank you for your time. ... View more