why is the result of (start, end) different from calculated result in PHREG?

[medic]

Hi,
I'm using a PROC PHREG to manage survival data.
Since explain variable is time-dependent, I coded as:
(start, end)*censor(0)=variable

I also made another dataset by manually calculating the time to event period (tte = end - start) because the original code takes too long to process, and ran the following code:
tte*censor(0)=variable

But the results from those two codes are different, although I think the only difference is that I already calculated the result of "(start, end)".

Can anyone explain why this is happening?

Thanks a lot in advance!

[ballardw]

I suspect that we would need to see actual input data (both versions) and the entire proc phreg code used for both to get enough details.

And which result and by how much difference?

[medic]

Thanks.

Here are some examples of my data structure.

Say the study period is until 2013-12-31 as in ID 1.

But if there's a change in any subject due to some time-dependent variable (treatment / as in ID 2 and 3),

I updated the attribute before and after the date of the change as in Table 1.

Table 1.

ID	startdate1	enddate1	treatment1	outcome1	startdate2	enddate2	treatment1	outcome2
1	2013-05-01	2013-12-31	0	0	.	.	.	.
2	2013-06-01	2013-06-30	0	0	2013-06-30	2013-11-20	1	0
3	2013-07-01	2013-07-30	0	0	2013-07-30	2013-12-01	1	1

In order to run this through PROC PHREG, I changed the dataset into long form as following table 2.

(i.e, those who have different states have 2 rows)

Table 2.

ID	start	end	treatment	outcome
1	2013-05-01	2013-12-31	0	0
2	2013-06-01	2013-06-30	0	0
2	2013-06-30	2013-11-20	1	0
3	2013-07-01	2013-07-30	0	0
3	2013-07-30	2013-12-01	0	1

and the code goes as:

proc phreg data=sample;

class treatment (ref='0');

model (start, end)*outcome(0) = treatment / rl;

strata OOO (some other adjusting variables);

run;

But when I run this code, it takes several hours to get the results. (original dataset has about 10 million records)

So instead using (start, end) form, I manually calculated the time-to-event (tte) as following table 3

Table 3.

ID	tte	treatment	outcome
1	244	0	0
2	29	0	0
2	143	1	0
3	29	0	0
3	124	0	1

and only changed the (start, end) part into "tte" as :

proc phreg data=sample;

class treatment (ref='0');

model tte*outcome(0) = treatment / rl;

strata OOO (some other adjusting variables);

run;

In this case, the program only takes minutes, but the results are different from when using (start, end) statement.

(sorry that I don't have exact numbers since I'm running another program right now)

* I referred to 

http://support.sas.com/resources/papers/proceedings12/168-2012.pdf

this article when managing the dataset, though it doesn't say anything about whether manually calculating the time-to-event will result the same or not.

hope this explains enough to ask for your help.