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Skalski, J.R.
Estimating wildlife populations based on incomplete area surveys
1994  Wildlife Society Bulletin (22): 192-203

Area surveys of animal resources are typically based on a 2-stage nested sampling design. The first stage is the selection of a subset of possible study plots within the region of inference. The second stage then consist of surveying animal densities at the plots selected in the first stage. Consequently, both sampling error associated with subsampling the region and measurement error associated with the survey method contribute to the variance of estimates of total abundance and mean density. Sample size calculations need to take into account both of these error sources in the design of area surveys. Use of sampling with probability proportional to size (SPPS) is recommended over simple random sampling (SRS) when study plots are of unequal size. When plots vary in size, SPPS typically will result in a smaller variance. However, when plots are of equal size, SPPS and SRS are equivalent. Stratified sampling designs also are suggested to help reduce the variance of area survey results. Appendices A and B show variance formulae for finite sampling methods must be modified to account for error in animal densities measurements. Unless adjustments in the variance estimate are incorporated, classical finite sampling procedures will underestimate the actual variance in area surveys of wildlife. The consequence would be a false of precision and the failure to appreciate the uncertainty of resource management decisions.

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