Hi
can anyone help me with what is either a MARK vs MSurge estimation difference, or (more likely) my inability to write GEMACO coding.
I would like to use MSurge for my current analysis as its coding flexibility is appealling since I may get into quite complicated models as I explore the data more fully, however I find the model definition language quite a challenge. I though I'd worked out how to code for a simple age structure, but when I compared the output to that from MARK, where I am more sure of the model structure, I had (noticeably) different parameter estimates. Here are the details:
Both sexes of birds have been first ringed in 3 age classes (juv, yearling, adult), giving 6 groups. I have been trying to fit a constant age-related survival model, where juveniles have 3 age classes (say parameters 1,2,3), yearlings have 2 (paras 2,3) and adults one (para 3). So as juvs and yearlings get older they contribute to the appropriate age survival estimates. In MARK this is straightforward to achieve using the PIMs and I am confident that part is right. I thought I had it right in MSurge too, using the following coding, adapted from the MSurge manual (pg15):
for males
a(1).[g(1)] + a(2).[g(1)&g(2)] + a(3).[g(1)&g(2)&g(3)]
and the same for females but substitute g(4-6) for g(1-3)
but I get different results:
MARK
0.914
1.0
0.89
1.0
0.68
0.82
MSurge
0.92
0.99
0.87
0.94
0.88
0.84
while most of these are similar, p4 and p5 are quite different. When I run simpler constant rate models I get more or less identical results, which suggests its my coding which is at fault, but I have tried all the combinations I can thnk of and have run out of ideas.
all help gratefully received,
Mark