Stratified Petersen Analysis System in R

Versions and installation

devtools::install_github("cschwarz-stat-sfu-ca/SPAS", dependencies = TRUE,
                        build_vignettes = TRUE)


This is an R version of the Windoze program SPAS to estimate population abundance using a Stratified Petersen Estimator (Darroch 1961; Plante et al 1998; Schwarz and Taylor, 1998)

The user is allows to pool rows and/or columns prior to analysis but the number of rows must be less than or equal to the number of columns (s <= t). The conditional likelihood formulation of Plante et al (1998) is used to estimate the parameters.

Because the data are physically pooled prior to analysis, it is not yet possible to compare different poolings to see which is most appropriate - this is under active investigation. A good discussion of how to decide on pooling rows/columns is found in Schwarz and Taylor (1998).


Darroch, J. N. (1961). The two-sample capture-recapture census when tagging and sampling are stratified. Biometrika, 48, 241–260.

Plante, N., L.-P Rivest, and G. Tremblay. (1988). Stratified Capture-Recapture Estimation of the Size of a Closed Population. Biometrics 54, 47-60.

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.