I am working in the context of opt-in, web-based surveys. Often the desire is for accurate population estimates, and often at a country-wide level. The standard approach at this organization is to define demographic strata and determine quotas for each stratum according to high-quality reference data such as that from the U.S. Census Bureau, so that strata proportions equal population proportions. Most often these strata are defined by gender and age.
I've come to understand that some of the surveys run here are pre-stratified at one combination of gender and age groups, and then after the survey timeline has ended, post-stratified and weighted along more discretized groupings of the same variables. As an example, assume that pre-collection strata are divided along 3 age groups (18-24, 25-54, 55+), and then post-collection strata are divided into 6 age groups (18-24, 25-34, 35-44, 45-54, 55-64, 65+). Quotas are set for the initial strata according to census data, and then the results obtained from this quota sample are weighted according to the same census dataset, but divided into narrower age groups.
Something about this feels wrong to me, but I don't have the expertise to identify what exactly that is. Reading about survey methods, I see plenty of material about pre-stratification and post-stratification, but nothing on using them both together. Maybe my attempts to find reading on this particular approach are inadequate. Either way, I would very much appreciate some guidance here.
Thank you in advance.