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2007 Los Angeles 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 2007 LACHS is the fifth in a series, following surveys conducted in 1997, 1999, 2002 and 2005. Each LACHS has included an adult component and a child component, administered to the parent or guardian (usually the mother) of a child 0-17 years old. Recent surveys have also included 7 or 8 subsample sections, each administered to a portion of the adult survey population.

The purpose of the health survey is to provide 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. 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 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 2007 Los Angeles County Health Survey (LACHS) was commissioned by the Los Angeles County Department of Public Health and was conducted by the Field Research Corporation. Data collection occurred from April 2007 to January 2008. Funding for the survey was provided by grants from First 5 LA and the Department of Public Health Tobacco Control and Prevention Program, Emergency Preparedness and Response Program, Alcohol and Drug Program Administration, Office of AIDS Programs and Policies, and the Maternal, Child, and Adolescent Health program.

Sample Size: A total of 7,200 adults (ages 18 years or older) residing in Los Angeles County were interviewed for the Adult survey. In addition, 5,728 interviews were conducted among the parents (primarily mothers) of children ages 17 years or under. Respondents in each household were randomly selected using an unrestricted random digit dial sampling methodology, which included all eligible LA County households with landline telephones.

Languages: Interviews were conducted in English, Spanish, Chinese (Mandarin and Cantonese), Korean and Vietnamese. Over one quarter (26%) of all interviews in the 2007 LACHS Adult Survey were completed in non-English languages, while over four in ten parents (43%) 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: The overall cooperation rates for adult and child surveys were 40% each, meaning that 40% of the people who answered the phone were willing to complete the interview with the surveyor. Notably, the 2007 LACHS incorporated a pre-approach letter, which notified households whose phone numbers were randomly generated for the survey that they would receive a call from the County Department of Public Health. The cooperation rate of households mailed the pre-approach letter was nine percentage points higher (47%) than those that were not mailed the letter or whose letter was returned as undeliverable (38%).

Response Rate: The response rate is the number of completed survey interviews divided by the total number of phone numbers selected for the survey sample, including non-residential numbers, numbers where contact with a household member was never achieved, and numbers where the person who answered the phone did not wish to begin or complete the survey. The 2007 LACHS response rate was 18% for the Adult Survey and 15% for the Child Survey (including homes ineligible because no children resided there.) The response rates achieved in the 2007 LACHS were lower than those achieved in earlier LACHS studies in 2002 (31.1% Adult, 33.9% Child), and 2005 (22.8% Adult, 26% Child).

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 2007 LACHS have yielded accurate and reliable data for both the Adult Survey and the Child Survey.

For more detailed information about the 2007 Los Angeles County Health Survey methods, please see our full methodology document.

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Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.
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