comp.soft-sys.sas - The SAS statistics package.
Hello, I have baseline and follow-up values for my intervention and control group. I want to conduct a difference-in-difference analysis. Y is continuous. i.e. Y = b0 + b1*Time + b2*Intervention + b3*(Intervention*Time) +b4Xn where Time is an indicator if the value is obtained at follow-up (1, 0) Intervention is an indicator for being in the intervention group (1,0) Intervention*TIme is the interaction Xn: vector of all my other covariates. I understand the theory pretty well, but have not been able to find the SAS code to conduct this analysis. Pl. advise on 2 things: 1. How to arrange the data i.e. one line person or one line per person per time period? 2. The code of course. Do you use PROC GENMOD or just PROC REG? I just heard about the LISTSERV, and the resources available, so I'm new to this forum. Thanks in advance for taking the time -- MG
Hello everyone, >i have fitted a piecewise linear model using GEE for repeated measurements >with binary outcome - following is the code. > >Time takes 1, 2, ..., 10,11 >and after time=6 the intervention started, so >st1=min(time,6) and >st2=max(0,time). > >I am trying to test whether coefficients for st2*interv is significantly >different from st1*interv (whether rate of change is different by >intervention over time - the difference of difference). so i wrote the >following program but can't get the estimate from SAS Genmod. proc genmod data=ppnewnw.co_&pr order=data; class decid time interv; model co_&pr._n/co_&pr._d= st1|interv st2|interv / dist=binomial link=logit dscale lrci; estimate "st1*interv vs. st2*interv" st1*interv 1 0 st2*interv -1 0/e; repeated subject=decid / type=ar(1) corrw covb; title "&pr. - Binomial Piecewise Linear GEE Model for Balanced Sample/&vr"; run;; I then recoded st1 as 1, 2, 3,4,5,6,7,8,9,10,11 and st2 as 0, 0, 0, 0, 0, 0, 7, 8, 9, 10 , 11. But both st1*trt and st2*trt are not significant this time - my concern is that st1 and st2 are highly correlated (0.9) so that it covers each other's effects. I wonder if any one can offer some insight as how I may be able to do the test. Thank you very much. I was kindly informed that by attaching an html file, i may have caused trouble to many people. I was not aware of it before so please accept my apology here. elena
Hi, I want to calculate the difference between diag date and each date of service for each pt. following is the sample of data of 3 pt : pt diag_dt sev_dt dif 1 10APR2006 05JUN2006 56 1 10APR2006 06JUN2006 57.425694346 1 10APR2006 07JUN2006 58 2 19AUG2005 19JUN2007 669.7414341 2 19AUG2005 27JUN2007 677.73304367 3 16OCT2006 13NOV2006 28 3 16OCT2006 20NOV2006 35 3 16OCT2006 27NOV2006 42 I calculated the difference between two dates and got the dif values but I am not sure why few values are having decimals and not just the number. following is the code I used: dif= (diag_dt-sev_dt); Please advise if I have to use any function to calculate the difference where I can get values with out decimals. thank you, Gopi.
Hi, I have a variable called vismin which has values from 1 to 5 indicating different visible minority categories. I want to carry out a test of the null hypothesis that the coefficients of my explanatory variables are the same for different regressions (i.e. B1=B2=B3=B4=B5). I don't know if I can use my variable vismin or if I should create 5 difference dummy variables and use that? I thought I could use a proc logistic, but it seems we an only use that for one regression, not when comparing the 5 regressions. Any thoughts? Thanks.