topic Re: how does SAS understand time in Statistical Procedures

how does SAS understand time

Lorraine22 — Wed, 02 Jun 2021 10:07:35 GMT

Hi all

I am comparing proportion of people who attend a clinic between two different time periods.

the two time periods are different in length – one is 3-months; the other is 9 months.

I would like to ask how do I tell SAS the time (or how does SAS understand what my time is) - in my code I have entered 3 for 3 months and 9 for 9 months - is this correct - would appreciate any advice

thanks

data Non_urg(keep=time case log_t);

infile datalines;

input time case pop;

log_t=log(time);

output Non_urg;
datalines;

9 144 1574
3 76 916

;

proc genmod data=Non_urg;

model case=time/ dist=poisson link=log offset=log_t;

run;

Re: how does SAS understand time

PaigeMiller — Wed, 02 Jun 2021 10:37:46 GMT

SAS understands that 3 is different than 9, and that 9 is six greater than 3, and so on.

Nothing you have done here indicates to SAS that these are time intervals or times, nor is that necessary to use PROC GENMOD properly.

Re: how does SAS understand time

Lorraine22 — Wed, 02 Jun 2021 12:00:25 GMT

thanks for replying to my message

my understanding is that I don't need the offset if the two time periods were the same length; but I need to use it when time periods are different lengths.

so how do I indicate to SAS that they are time periods if my code is not correct. can you explain more how I use the proc genmod properly

appreciate your time - its been a while since I've used SAS

thanks

Re: how does SAS understand time

PaigeMiller — Wed, 02 Jun 2021 12:04:10 GMT

As far as I can see, your code is correct.

Re: how does SAS understand time

Lorraine22 — Wed, 02 Jun 2021 12:08:35 GMT

can you explain your reply from earlier "Nothing you have done here indicates to SAS that these are time intervals or times".

I'm trying to understand how to indicate to SAS that they are time intervals.

is it by the inclusion or exclusion of the offset?

Re: how does SAS understand time

PaigeMiller — Wed, 02 Jun 2021 13:08:06 GMT

@Lorraine22 wrote:
can you explain your reply from earlier "Nothing you have done here indicates to SAS that these are time intervals or times".

I'm trying to understand how to indicate to SAS that they are time intervals.

is it by the inclusion or exclusion of the offset?

Here is an example of Poisson regression in SAS: https://documentation.sas.com/doc/en/pgmsascdc/9.4_3.4/statug/statug_genmod_gettingstarted01.htm

It seems to me your code is correct, and that you don't have to do anything else. There is no such thing as an "interval" in SAS, you don't have to specify that something is an "interval" (and in fact, you can't indicate that anyway).

Re: how does SAS understand time

Lorraine22 — Wed, 02 Jun 2021 15:37:03 GMT

great - thanks for your help