Methodology
In general terms, the Association retail fuel survey designs utilize an area (survey areas, strata and/or cluster) random sampling methodology with probability proportional to size (PPS). PPS sampling generates self-weighting samples that would represent the fuel sold within each area without bias. In some programs the regulations may specify sampling with certainty be incorporated in the survey designs.
The quantity of sampling and where samples are procured are determined by the regulations and the specific program objectives outlined in the respective survey design plan documents. In all cases the survey design plans are reviewed annually and approved by the appropriate Federal and/or State environmental agencies charged with compliance/enforcement.