OPM uses three different types of categories: Major expenditure groups, primary expenditure groups, and detailed expenditure categories.
(a) Major expenditure groups. OPM groups expenditures into nine major expenditure groups (MEGs). These categories are food, shelter and utilities, clothing, transportation, household furnishings and supplies, medical, education and communication, recreation, and miscellaneous.
(b) Primary expenditure groups. OPM subdivides each MEG into primary expenditure groups (PEGs). There are approximately 40 PEGs.
(c) Detailed expenditure categories. OPM further subdivides each PEG into other categories down to the detailed expenditure categories (DECs), which are generally equivalent to the most detailed level of tabulated CES categories. OPM classifies each DEC into one of the PEGs to aggregate DECs with similar demand and cost characteristics into PEGs. Alternatively, OPM may remove the DEC entirely from the list of expenditures. Therefore, the classification of the DECs into PEGs and sub-PEGs does not necessarily follow that used in published CES tables.