Post-stratification as a bias reduction technique

Opportunistic, non-random surveys often provide information for management of wildlife resources, yet managers may be seriously misled due to biases in the data. Post-stratification may be used to reduce bias. For a given factor of interest, a variable is identified that correlates well with it. Observations on the variable are ordered, and strata are defined by determining appropriate cutpoints. The variable might be an estimator of the factor itself, or estimated from the same data as are used to estimate the factor, and evaluated for each of a number of small geographic units. Post-stratification can be applied to obtain an estimate of each component for a random point in the area occupied by the resource, and bootstrapping may be used to yield a robust variance of the composite estimate that does not require the assumption that the component estimates are uncorrelated. -from Authors