Given budgetary limitations, we surveyed a stratified,
random sample from this population. We
stratified by health condition based on power
calculations for condition-specific outcomes for
another portion of the overall study. For example,
the sample size for persons with hypertension was
based on the number to detect clinically meaningful
differences in blood pressure level. Attempting to
get better representation for the overall study of
groups with particular national policy importance,
we oversampled the following groups: 1) those
without a prescription benefit through the plan; 2)
persons with Medicaid; and 3) persons likely to
have low incomes (estimating income by geocoding
addresses to census block groups). Of the 5533
enrollees selected for surveying, 4763 persons
responded for an overall response rate of 86%