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Los Angeles County
Department of Public Health
Health Assessment Unit
313 N. Figueroa St., Room 127
Los Angeles, CA 90012
Phone:(213) 240-7785
Fax:(213) 250-2594

2011 L. A. County Health Survey Background Summary & Methodology

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 to identify 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 2011 LACHS is the sixth iteration of the LACHS study (1997, 1999, 2002, 2005 and 2007). Each LACHS has included an adult component and a child component, administered to the parent/guardian or primary caretaker of a child 0-17 years old. Each survey included 7 or 8 subsample sections, each administered to a portion of the adult survey population. The most recent 2011 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 2010, an estimated 21.7% 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 2011 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 15, 2010 to June 18 2011. 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's  Tobacco Control and Prevention Program, Emergency Preparedness and Response Program, Substance Abuse Prevention and Control, and Environmental Health. 


Sample Size: A total of 8,036 adults (ages 18 years or older) residing in Los Angeles County were interviewed for the Adult survey (6,686 landline and 1350 cell phone interviews). In addition, 6,013 interviews were conducted among the parents/guardians or primary caretakers of children ages 17 years or under (5745 landline and 268 cell phone interviews). Respondents in each household were randomly selected using a dual overlapping design including a random digit dial (RDD) sample frame of all eligible LA County households with landline telephones, as well as a cross-sectional, RDD cell phone sample frame of telephone numbers from LA County (based on county of the billing office). The sample design was considered "overlapping" because households that have both landline and cell phone service have a probability of being selected from both frames. The degree of "overlap" between the frames is accounted for in the weight calculations. Telephone numbers from each frame were managed independently.

Languages: Interviews were conducted in English, Spanish, Chinese (Mandarin and Cantonese), Korean and Vietnamese. About one fifth (19.5%) of all interviews in the 2011 LACHS adult survey were completed in non-English languages, while three in ten (30.6%) were interviewed in a non-English language as part of the 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, appropriate weights were developed to account for differences in the probability of selection of households into each sample and to align the survey results to known geographic and demographic characteristics of the County’s adult and child populations. This process involved calculating a household weight and a population rate for each individual record, and projecting the data files to the population of residential housing units and the population of non-institutionalized adults and children in Los Angeles County.

Cooperation Rate: In the 2011 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 rate was 59.2% for landline survey, 70.8% for the cell phone survey, and 65.6% combined. For the child survey, the cooperation rate was 62.1% for landline survey, 72.1% for the supplemental landline survey, 59.3% for the cell phone survey, and 64.0% combined.

 Response Rate: In the 2011 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 34.8% for the landline survey, 23.1% for the cell phone survey and 28.4% combined. For the child survey, the rate was 21.7% for the landline survey, 30.2% for the landline supplemental survey, 13.6% for the cell phone survey, and  20.2% combined. The response rates achieved in the 2011 LACHS were better than those achieved in the 2007 LACHS (18% Adult, 15% Child).

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 new survey procedures employed in the implementation of the 2011 LACHS have yielded accurate and reliable data for both the Adult Survey and the Child Survey.

For more detailed information about the 2011 Los Angeles County Health Survey methods, please see our full methodology document.
 

1 National Center for Health Statistics. 2011a. Wireless Substitution: Early Release of Estimates from the National Health Interview Survey, January -June 2011. http://www.cdc.gov/nchs/nhis.htm.

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/cell_phone_task_force_report.htm

Topics of 2011 Health Survey

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