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The California Health Interview Survey (CHIS) uses a two-stage, geographically stratified random-digit-dial (RDD) design to produce a sample that is representative of the California population.
In the first stage, a sample of randomly generated telephone numbers is drawn by computer for 44 predefined geographic areas or "strata" (41 of these strata are individual counties; 3 strata are groupings of counties with smaller populations). These telephone numbers are then dialed to determine if they are households and thus eligible for the survey.
In the second stage, one adult is randomly selected to be interviewed from among all adults living in the household. Only the selected person is eligible for the extended adult interview. If there are eligible children in the household, additional interviews of adolescents (age 12 to 17) and about children (age 0 to 11) are attempted.
CHIS oversamples rural counties that have small populations and includes multiple techniques to achieve statistically robust samples of several ethnic population groups. Details are available at the links below.
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Sample Size by County and Race/Ethnicity (PDF, 311k) |
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Sample Design Description (PDF, 55k) |
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Sample Design Description (PDF, 176k) |
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Sample Size by County and Race/Ethnicity (PDF, 181k) |
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Sample Design Description (PDF, 187k) |
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Sample Size by County (PDF, 305k) |
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Sample Size for Berkeley, Long Beach, and Pasadena (PDF, 16k) |
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Sample Size by Race/Ethnicity (PDF, 308k) |
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