Calculate the average result for each subgroup. For example, suppose you were looking at public support for a certain policy. You might find that it had the support of 60 percent of Democrats, 50 percent of independents, and 40 percent of Republicans.
Calculate the proportion each subgroup represents of the total population. In the example being used here, Republicans might represent 40 percent of the population, Democrats might also be 40 percent, and independents might be 20 percent of the population.
Multiply the average of each subgroup by the proportion that subgroup represents of the total population. In this example, total Democratic support would be 60 percent times 40 percent, or 24 percent. Total Republican support would be 40 percent times 40 percent, or 16 percent, and total independent support would be 50 percent times 20 percent, or 10 percent.
Add up the total percentages for each subgroup to find the aggregate average. In this example, 24 percent Democratic support, 16 percent Republican support and 10 percent independent support would add up to 50 percent total public support.