State policymakers regularly rely on the integrity of CHIS data. We have hard decisions to make and now, more than ever, this data is essential to the well-being of the people of California.

Diana Dooley, Former Secretary, California Health and Human Services Agency

The California Health Interview Survey (CHIS) began in 2001 as a biennial population-based, omnibus health survey of Californians. CHIS became a continuous survey in 2011, with ongoing data collection throughout a two-year cycle, that has enhanced CHIS’ role as a critical and timely source of public health surveillance information for California. 

CHIS is a mixed-mode (web and telephone) survey that uses an address-based sampling (ABS) frame, making it representative of the state’s population. Prior to 2019, CHIS was a telephone survey that used a dual-frame, random-digit-dial (RDD) technique.

CHIS randomly selects one adult to interview in each randomly sampled and participating household throughout California. In addition to adults, interviews are conducted about the health of children (ages 0–11, by proxy with an adult sufficiently knowledgeable about the health of the selected child) and adolescents (age 12–17, directly interviewed following parental permission). CHIS data can be analyzed at the county level for the state's 41 most populated counties. The remaining 17 counties are combined into three different groups.

Overall, the CHIS sample is designed to provide population-based estimates for most California counties and all major ethnic groups, including several ethnic subgroups. 
The sample is designed to meet and optimize two goals: 

  • To provide local-level estimates for counties with populations of 60,000 or more for local planning and comparisons among counties; 
  • To provide statewide estimates for California’s overall population, its major racial and ethnic groups, as well as for several Asian and Latino ethnic groups.

CHIS provides access to detailed design plans and sample sizes by county, age, and race and ethnicity for all years.

Download actual sample numbers and the design plans for achieving sampling goals below: