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
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