Abstract: Computer systems, computer program products and methods for surveying a target population are provided. A survey instrument is fielded to a sample population of the target population, where individual members in the sample population are selected from the target population such that the distribution of members in the sample that start the survey instrument provides a probability sampling of the target population for at least one stratification variable. A qualifying population is identified from the sample, where each member in the qualifying population qualifies for the survey instrument based on a response to one or more screener questions in the survey instrument. A total number of members is determined within the target population that the qualifying population represents based on a comparison of the distribution of the qualifying population and the distribution of the target population with respect to the at least one stratification variable.