Royle Biometrics average & total abundance

[rak]

Hello
This is a very elementary question, but I cannot find any previous posts about it. I'm using Presence 3 to run Royle Biometrics point count abundance analyses. When I include a site specific covariate, results show site-specific estimated lambdas (abundances), then avg. estimated abundance, then total abundance. I'm perplexed that the average lambda estimate printed in the summary does not equal the average of the site-specific lambdas printed above, nor does the total abundance estimate match the sum of the site-specific lambdas printed above. Instead the printed average and total seem to correspond to what would be calculated if the average equaled the lambda for site 1. Below is example output using the UVM spreadsheet data (just 1 site specific covariate, no survey specific covariates), for which I obtain an average lambda = 7.31 and a total estimated abundance = 146. I apologize in advance if I'm missing something very basic, but would be greatful for help:

Individual Site estimates of Lambda:
Site Survey Lambda Std.err 95% conf. interval
1 site 1 1-1: 8.5273 4.7042 4.6964 -40.8254
2 site 2 1-1: 8.7172 4.8690 4.7296 -42.2384
3 site 3 1-1: 8.8817 5.0175 4.7516 -43.5093
4 site 4 1-1: 8.7423 4.8913 4.7333 -42.4298
5 site 5 1-1: 8.6198 4.7835 4.7136 -41.5058
6 site 6 1-1: 6.2557 3.3592 3.5549 -29.1746
7 site 7 1-1: 6.3996 3.4087 3.6699 -29.6106
8 site 8 1-1: 6.6946 3.5250 3.8881 -30.6286
9 site 9 1-1: 7.0997 3.7179 4.1477 -32.3090
10 site 10 1-1: 7.0896 3.7126 4.1418 -32.2632
11 site 11 1-1: 7.9233 4.2305 4.5315 -36.7467
12 site 12 1-1: 6.1676 3.3311 3.4818 -28.9264
13 site 13 1-1: 6.4865 3.4409 3.7367 -29.8929
14 site 14 1-1: 7.8973 4.2119 4.5222 -36.5864
15 site 15 1-1: 5.9954 3.2810 3.3334 -28.4810
16 site 16 1-1: 7.0587 3.6966 4.1236 -32.1238
17 site 17 1-1: 6.3923 3.4061 3.6642 -29.5876
18 site 18 1-1: 6.7578 3.5525 3.9316 -30.8687
19 site 19 1-1: 7.1687 3.7547 4.1873 -32.6288
20 site 20 1-1: 7.3361 3.8487 4.2775 -33.4441

============================================================

MODEL PARAMETERS:
Estimated parameter estimate std.err 95% confidence interval
-------------------------- -------- ------- ------------------------
Detection probability (c) = 0.1778 0.0935 -0.0055 - 0.3611
Avg. abundance/sample unit(lambda) = 8.53 4.70 -0.69 - 17.75

Derived parameter estimate std.err 95% confidence interval
-------------------------- -------- ------- ------------------------
Occupancy (psi) = 0.9998 0.0009 0.9980 - 1.0016
Total Abundance (N) = 170.55 94.08 -13.86 - 354.95

[jhines]

Hi,

You're right about the estimates that are printed out at the end. The are based only on the first site when there really should be a different estimate for each site when you have site covariates. The only problem is what to do with the derived parameter estimate, N. We probably don't want to print an estimate of N for each site. I've talked with Darryl about this and his suggestion was to sum the lambda's to get N. I'll work on incorporating this into the program soon.

Cheers,

Jim