Dear All, We are analyzing data from a cohort of participants with a high risk of HIV infection. At this moment, our focus is on sexually transmitted disease infection. Given that patients in our cohort may have more than one sexually transmitted disease, we are considering using a frailty model. We are currently thinking of using the COX Regression model, but I would like to check if the data structure I am creating is correct.   The structure of our database would incorporate time-dependent variables. Here we have the data for three participants. The observation of the participant 1 (ID=1) is censored at the first visit, then he experiences the event at the second visit, and does not return. The second participant experiences several events while the third one is censored at all visits. ID  TSTART TSTOP STATUS  1         0           91         0 1        91        187        1 2         0          115       0 2         115       210      1 2         210       321      0 2        321        430      1 2        430        542      1 3        0            122      0 3        122       312       0 3       312       431        0   The other issue I wanted to address is how to decide on the distribution of the random parameter associated with frailty. Is there a specific test for this? Thank you.. Best regards, Iuri leite   ... View more

Dear Colleagues, I am inquiring to know if it is possible to execute a survival random forest analysis using SAS. I have been examining the PROC HPFOREST procedure, but I have not encountered any features related to survival analysis within this context. I have come across a paper wherein survival was considered using a discrete-time logistic regression model. Thank you in advance. Best regards, Iuri Leite ... View more

  Dear all, I am analyzing a dataset from a cohort of participants in which we observe if they develop specific infection at each quarterly visit. In this dataset a significant number of participants developed the disease more than once. Initially, we used a hazard model considering the time until the first occurrence of the infection. However, we are now interested in identifying factors associated with more than one occurrence of the disease. Specifically, in the case of two infections, the individual is identified with an infection at a specific visit, receives treatment and then in another visit, the disease is identified again. Since time is an important element, is it possible to conduct a survival analysis in this case? Is it possible to conduct a survival considering an ordinal response?  Thank you in advance. Best regards, Iuri Leite ... View more

Dear Friends,   I am writing to ask if there is anyway for me to run a exact GEE logistic regression in SAS? I am running it using PROC GENMOD.   PROC GENMOD DESCENDING; CLASS COPID WEEK (REF='0') COUNTRY (REF='BR'); MODEL HEPAT_B=WEEK COUNTRY/ DIST=BIN LINK=LOGIT; REPEATED SUBJECT=COPID/TYPE=UN; ESTIMATE 'TIME' WEEK 1 -1/EXP; RUN;   WEEK is a dichotomous variable and when WEEK IS 1 HEPAT_B is always zero. When a use a logistic exact model I am able to estimate the effect of week. But when I run the GEE logistic, the model do not estimate the effect of week.   I could not see any option for exact logistic. Thank you in advance. Regards,   Iuri ... View more

Dear All,   I run a model in which a have one variable (Var1) interacting with three other variables (Var2, Var3 and Var4). Var1 has three categories and Var2, Var3 and Var4 are binary variable indicating the presence or absence of symptoms. Is it possible to suggest a text showing the best way to interpret interactions of one variable with two or more variables? Thanks a lot. Regards,   ... View more