by **constant survivor** » Thu Nov 26, 2020 11:19 am

Hi,

I got one further question concerning CONTRAST.

I got significant results for a test of weighted average estimates of Species x vs. Species y. Say, two groups, right?

On the web page it says:

"Contrast then tests the null hypothesis that the average survival for each group is the same"

What irritates me, is that when I tried to calculate the mean survival for the same two species with the Method of Moments approach (VC estimation and so on... ; see other thread) I had strong difficulties to estimate a mean because of obviously sparse data. My aim of this surely was, to compare those means.

In terms of interpretation this brings me into the situation that I am on the one hand must admit, that calculation of mean survival for Species x and/or Species y is not possible because of sparse data (MOM approach).

On the other hand I am telling that there is a significant difference between the average survival of both species (CONTRAST).

I am aware about, that CONTRAST only compares the weighted average estimates I am feeding into it and that the MOM approach is based on the 'raw data' which surely is some different thing.

But how much certainty can this give me about real survival differences of both species? When the MOM approach is hardly even feasible and the result of CONTRAST is highly significant...

Is it just as simple as that one could say: it is not possible to calculate the 'true' mean so I made a compromise and compared the weighted average estimates?

Any thoughts on that are highly appreciated.

Thanks

Hannes