Ongoing assessment of the health status of the population is a core function of local health departments, and improving the availability of high quality health information remains a major priority for the Los Angeles County Department of Public Health (DPH). The Office of Health Assessment and Epidemiology (OHAE) within DPH is charged with carrying out this assessment function by collecting and disseminating population-based health information to plan, evaluate, and develop policy, and to serve local communities and agencies engaged in improving the health status of LA County residents.

The Los Angeles County Health Survey (LACHS) functions as a primary vehicle for gathering information about access to health care, health care utilization, health behaviors, health status, and knowledge and perceptions of health-related issues among the LA County population. The survey provides updates on key health indicators and identifies emerging public health issues among adults and children residing in the County's eight service planning areas (SPAs) and 26 health districts. More importantly, the survey allows the Department of Public Health to track health issues over time. To properly address the root causes of poor health, the survey looks beyond risk factors for individual diseases to factors in the physical and social environment that influence health, such as land use, safety, poverty, and educational attainment. 

The 2015 LACHS is the seventh iteration of the LACHS; previous surveys were conducted in 1997, 1999, 2002, 2005, 2007 and 2011. Each LACHS edition includes an adult component and a child component, administered to the parent/guardian or primary caretaker of a child 0-17 years old. Each survey includes 7 or 8 subsample sections, individually administered to a portion of the adult survey population. The most recent 2015 iteration included a cell phone sample to improve sampling coverage due to the increased prevalence of households that do not have a landline telephone (in 2012, an estimated 31.7% of adults, and 36.7% of children under age 18 in Los Angeles County households did not have a landline telephone¹). Research shows that excluding the cell-only population can increase potential biases in survey results, since adults in cell-only households have different health outcomes and risk factors than adults residing in landline only households (Link et. al. 2007²).

The large sample size of each LACHS enables the survey to provide estimates not only of the health of the county population overall, but of people residing in the County’s many different geographic regions. The survey also provides valuable information about the health of the county’s major racial/ethnic sub-groups and numerous other demographic groups. Data are collected from households of all educational and income levels, including the most vulnerable residents living below the federal poverty level.

The 2015 Los Angeles County Health Survey (LACHS) was commissioned by the Los Angeles County Department of Public Health and was conducted by Abt SRBI Inc., an independent market research and public opinion firm. Data collection occurred from June 19, 2014 to June 2, 2015. Funding for the survey was provided by grants from First 5 LA, the Los Angeles County Department of Mental Health, and the Los Angeles County Department of Public Health programs including the Division of Chronic Disease and Injury Prevention, Children’s Medical Services, Emergency Preparedness and Response Program, Substance Abuse Prevention and Control, and Environmental Health. 

Sample Size: A total of 8,008 adults (ages 18 years or older) residing in Los Angeles County were interviewed for the Adult survey (5,026 landline and 2,982 cell phone interviews). In addition, 5,982 interviews were conducted among the parents/guardians or primary caretakers of children ages 17 years or under (3,632 landline and 2,350 cell phone interviews).

Languages: Interviews were conducted in English, Spanish, Chinese (Mandarin and Cantonese), Korean and Vietnamese. Approximately 15% of the interviews in the 2015 LACHS adult survey were completed in non-English languages, while about 22% were interviewed in a non-English language as part of the 2015 child survey.

Weighting: Statistical weighting is utilized to generalize the sample survey data to the overall LA County population. For adult, child, and subsample data files, population and household weights were created. Population weights were developed by calculating a design weight, a compositing factor to account for the overlapping dual frame design, and then raking to population control totals. Household weight were developed by converting the population weight to an initial household weight, then raking to household-level control totals.

Cooperation Rate: In the 2015 LACHS, the cooperation rates were calculated separately for the landline and cell phone versions of the adult and child surveys based on guidelines provided in AAPOR's Standard Definitions3. For the adult survey, the cooperation rate was 69%, and for the child survey, the cooperation rate was 73%.

Response Rate: In the 2015 LACHS, response rates were calculated following guidelines provided by AAPOR's Standard Definitions² and the AAPOR Cell Phone Task Force⁴ for calculating a single combined response rate from overlapping dual frame surveys. For the adult survey, the response rate was 15%, and for the child survey, the response rate was 16%.

Note About Response Rates:

Declining response rates are not just a problem for the LACHS, but for all telephone surveys conducted by the leading survey research organizations in the U.S. in recent years. In Los Angeles County, telephone surveys are particularly difficult to execute. While we understand that lower response rates are not ideal, we believe that the survey procedures employed in the implementation of the 2015 LACHS have yielded accurate and reliable data and that the survey sample closely mirrors the Los Angeles County population for both the Adult Survey and the Child Survey.

For more detailed information about the 2015 Los Angeles County Health Survey methods, please see our full methodology document.
 

1. National Center for Health Statistics. 2013. Wireless Substitution: State-level Estimates from the National Health Interview Survey, 2012. http://www.cdc.gov/nchs/data/nhsr/nhsr070.pdf

2 Link, M.W., Battaglia, M.P., Frankel, M.R., Osborn, L., and Mokdad, A.H. 2007. Reaching the U.S. Cell Phone Generation: Comparison of Cell Phone Survey Results with an Ongoing Landline Telephone Survey. Public Opinion Quarterly, 71: pp. 814-839.

3. Standard Definitions: Final Dispositions of Case Codes and Outcome Rates for Surveys. American Association for Public Opinion Research, 2011.Public Opinion Research, 2011.

4. New Considerations for Survey Researchers When Planning and Conducting RDD Telephone Surveys with Respondents Reached via Cell Phone Numbers. AAPOR Cell Phone Task Force Report, 2010. http://www.aapor.org/Education-Resources/Reports/Cell-Phone-Task-Force-Report.aspx

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