Hi, I can't figure out the reason for an unwanted result. Here is my code and result. Why VSSEQ=0.1 is behind VSSEQ = 2 and 3 in the result?  Thanks for your help!   data vitals; input VSSEQ VSTEST $ VISIT; datalines; 0.1 SBP 0 0.1 SBP 2 0.1 SBP 3 2 DBP 0 2 DBP 1 2 DBP 2 2 DBP 3 3 PULSE 0 3 PULSE 1 3 PULSE 2 run;   proc report data=vitals; column VSSEQ vstest visit; define VSSEQ /order ORDER=FORMATTED; define vstest /order order=data; define visit /order order=data; run;     ... View more

I am currently analyzing the impact of an intervention on medication numbers using difference-in-difference analysis, but I have encountered several challenges.   Following the SAS support instructions, I conducted the difference-in-difference analysis. However, I noticed a discrepancy between my results and SAS's example (Usage Note 61830: Estimating the difference in differences of means).   In the example, the value of 'Mean Estimate' in 'Contrast Estimate Results' is identical to the 'Estimate' in 'Least Squares Means Estimate'. However, in my case, these values were different. I suspect this could be due to my use of the negative binomial distribution with a log link, resulting in exponential values. Consequently, I am unsure whether to rely on the 'Mean Estimate' in 'Contrast Estimate Results' or the 'Estimate' in 'Least Squares Means Estimate', and how to interpret the results."   Contrast Estimate Results Label Mean Estimate Mean Confidence Limits L'Beta Estimate Standard Error diff in diff 1.51 1.49 0.41 0.0051   a*b Least Squares Means a b Estimate Standard Error z value Pr > |z| 1 1 0.77 0.00434 178.19 <.0001 1 0 0.03 0.00508 6.5 <.0001 0 1 0.72 0.00408 177.71 <.0001 0 0 0.40 0.00426 93.11 <.0001   Least Squares Means Estimate Effect Label Estimation Standard Error z value Pr > |z| time*hospitalize diff in diff 0.41 0.00509 81.01 <.0001 ... View more