Variance of stratified survey estimators with probability of detection adjustments

John Fieberg, John Giudice

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Estimates of wildlife population sizes are frequendy constructed by combining counts of observed animals from a stratified survey of aerial sampling units with an estimated probability of detecting animals. Unlike traditional stratified survey designs, stratum-specific estimates of population size will be correlated if a common detection model is used to adjust counts for undetected animals in all strata. We illustrate this concept in the context of aerial surveys, considering 2 cases: 1) a single-detection parameter is estimated under the assumption of constant detection probabilities, and 2) a logistic-regression model is used to estimate heterogeneous detection probabilities. Naïve estimates of variance formed by summing stratum-specific estimates of variance may result in significant bias, particularly if there are a large number of strata, if detection probabilities are small, or if estimates of detection probabilities are imprecise.

Original languageEnglish (US)
Pages (from-to)837-844
Number of pages8
JournalJournal of Wildlife Management
Issue number3
StatePublished - Apr 2008


  • Detection probability
  • Double sampling
  • Population estimate
  • Sightability adjustment
  • Stratified random sampling
  • Variance estimators


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