S+ Double-platform Line Transect Analysis Functions
These functions share some functionality with the double-platform analysis engine in Distance 5, which is written in R (a very similar language to S+). Some of the functionality of the Distance 5 software was checked by seeing that it produced the same estimates as that produced by these S+ functions. Nevertheless, there are differences between the two sets of code. Key differences are listed below.
Some things that these functions do which Distance 5 does not:
- They have the facility to use generalized additive models to fit flexible detection function forms.
- They do nonparametric bootstrapping for variance and confidence interval estimation.
- They allow automated variable selection with generalized linear model detection function forms.
Some things that Distance 5 does which these functions do not:
- Distance 5 allows "Point Independence" detection functions to be fitted; these functions only do the more restrictive"Full Independence" models. (see Buckland et al. 2004 for definition of terms)
- Distance 5 estimates variance and confidence intervals analytically.
Reference: 2004. Buckland, S.T., Anderson D.R., Burnham, K.P, Laake, J.L., Borchers, D.L. and Thomas, L. Advanced Distance Sampling. Oxford University Press; 416pp.
The functions were designed for use with S+ for Windows. They have not been tested on any other platform.
Download: Right-click S+DP.exe to download a self-extracting zip file containing:
- DOUBLE-PLATFORM SPLUS.HLP: Windows help file describing the set of functions and how to use them, together with some datasets.
- Double-platform Splus.CNT: Contents page for the Windows help file.
- dpfunctions: The functions themselves, saved using data.dump().
- dpegs: Example datasets for use with the functions.
Some papers which used the functions
2007. Southwell, C., Borchers, D.L., Paxton, C.G.M., Burt, M.L. and de la Mare, W. Estimation of detection probability in aerial surveys of Antarctic pack-ice seals. JABES 12: 41-54.
2004. Canadas, A., Desportes, G. and Borchers, D.L. The estimation of the detection function and g(0) for short-beaked common dolphins (Delphinis delphis), using double-platform data collected during the NASS-95 Faroese survey. Journal of Cetacean Research and Management 6: 191-198.
2004. Southwell, C., de la Mare, B., Borchers, D.L. and Burt, L. Shipboard line transect surveys of Crabeater seal abundance in the pack-ice off eastern Antarctica: evaluation of assumptions. Marine Mammal Science 20: 602-620.