Testing for Pooled Petersen

In SPAS: Stratified-Petersen Analysis System

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

Testing if a Pooled Petersen is appropriate

It is often of interest to know if a simple Pooled Petersen estimator, i.e., complete pooling over rows and columns, is appropriate.

As noted in Schwarz and Taylor (1998), the Pooled Petersen is unbiased under many conditions, but the most common are:

• Homogeneity of tagging probabilities, i.e. the probability of a fish being tagged in the release stratum is equal across all release strata.
• Homogeneity of recapture probabilities, i.e. the probability of a fish being recaptured is equal across all recovery strata.
• Complete Mixing, i.e. tagged fish mix completely with untagged fish.
• Correlation between tagging and recovery probabilities is zero, i.e. while probabilities are heterogeneous across fish, the two events are statistically independent.

We can examine the first of these conditions by examining the results of the stratified analysis and the results of a (logical) row pooling over all release strata.

Fitting the models

Reading in the data

This data were made available from the Canadian Department of Fisheries and Oceans and represent release and recaptured of female fish in the Lower Shuswap region.

test.data.csv <- textConnection("
  86   ,     54   ,     39   ,   219
  76   ,     35   ,     45   ,   168
  24   ,     53   ,     73   ,   190
1039   ,   1148   ,   2009   ,   0")

test.data <- as.matrix(read.csv(test.data.csv, header=FALSE, strip.white=TRUE))
test.data

We now fit several models

• A fully 3x3 stratified analysis
• Pooling over all rows using logical pooling
• Pooling over all rows using physical pooling
• Pooling over all rows and the last two columns using physical pooling
• Complete physical pooling over rows and columns (a classical Pooled Petersen)

Fully 3x3 stratified analysis

library(SPAS)
mod1 <- SPAS.fit.model(test.data,
                       model.id="No restrictions",
                       row.pool.in=1:3, col.pool.in=1:3)

SPAS.print.model(mod1)

3 Pooling over all rows using logical pooling

mod2 <- SPAS.fit.model(test.data,
                           model.id="Logical pooling to single row",
                           row.pool.in=c(1,1,1), col.pool.in=1:3, row.physical.pool=FALSE)

SPAS.print.model(mod2)

Pooling over all rows using physical pooling

mod3 <- SPAS.fit.model(test.data,
                           model.id="Physical pooling to single row",
                           row.pool.in=c(1,1,1), col.pool.in=1:3)
SPAS.print.model(mod3)

Pooling over all rows and last two columns using physical pooling

# do physical complete pooling 
mod4 <- SPAS.fit.model(test.data,
                           model.id="Physical pooling all rows and last two colum ns",
                           row.pool.in=c(1,1,1), col.pool.in=c(1,1,3))
SPAS.print.model(mod4)

Complete physical pooling (Pooled Petersen Estimator)

# do physical complete pooling 
mod5 <- SPAS.fit.model(test.data,
                           model.id="Physical complete pooling",
                           row.pool.in=c(1,1,1), col.pool.in=c(1,1,1))
SPAS.print.model(mod5)

Get the model objects fitted by TMB and create a report

model.list <- mget( ls()[grepl("^mod.$",ls())])
names(model.list)

report <- plyr::ldply(model.list, function(x){
   #browser()
   data.frame(#version=x$version,
              date   = as.Date(x$date),
              model.id         = x$model.info$model.id,
              s.a.pool         =-1+nrow(x$fit.setup$pooldata),
              t.p.pool         =-1+ncol(x$fit.setup$pooldata),
              logL.cond        = x$model.info$logL.cond,
              np               = x$model.info$np,
              AICc             = x$model.info$AICc,
              gof.chisq        = round(x$gof$chisq,1),
              gof.df           = x$gof$chisq.df,
              gof.p            = round(x$gof$chisq.p,3),
              Nhat             = round(x$est$real$N),
              Nhat.se          = round(x$se $real$N))

})
report

The AIC should be compared ONLY for the first two models because they are based on the same set of data. You cannot compare models that differ in the physical pooling

In this case, there is good evidence that the Pooled Petersen is too coarse because the goodness of fit statistic for the second model is very large (with a corresponding small goodness-of-fit p-value). Similarly, the AIC indicates that the model is 3x3 stratification (first model) is preferable to the model with complete row pooling (second model).

Notice that the estimates of the population size are identical under logical or physical row pooling (models 2 and 3). And how you pool columns (models 3, 4, 5) but assuming that the number of rows (after logical or physical pooling as long the number of rows is not larger than the number of columns) does not affect the population size estimate (or standard error).

References

Darroch, J. N. (1961). The two-sample capture-recapture census when tagging and sampling are stratified. Biometrika, 48, 241–260. https://www.jstor.org/stable/2332748

Plante, N., L.-P Rivest, and G. Tremblay. (1988). Stratified Capture-Recapture Estimation of the Size of a Closed Population. Biometrics 54, 47-60. https://www.jstor.org/stable/2533994

Schwarz, C. J., & Taylor, C. G. (1998). The use of the stratified-Petersen estimator in fisheries management with an illustration of estimating the number of pink salmon (Oncorhynchus gorbuscha) that return to spawn in the Fraser River. Canadian Journal of Fisheries and Aquatic Sciences, 55, 281–296. https://doi.org/10.1139/f97-238

SPAS documentation built on April 21, 2023, 1:10 a.m.