0545 Supporting Statement Part B 2014

Health and Diet Survey
OMB Control No. 0910-0545
SUPPORTING STATEMENT Part B
B. Statistical Methods
1.

Respondent Universe and Sampling Methods

The respondent universe for this collection of information will be non-institutionalized adults 18
and older who speak English or Spanish. Within the sampling universe, respondents will be
randomly selected from two sampling frames: a national landline telephone frame and a national
cell phone frame. More specifically, the Health and Diet Survey will adopt the overlapping dualframe approach as described by the American Association for Public Opinion Research, i.e., we will
select independent samples from random-digit-dialing frames that overlap in their coverage (e.g., a
landline frame and a cell phone frame) and we will not screen out dual-frame prospective
respondents (AAPOR 2010). Within a dual frame, we will include four groups of adults: (1) users
of landline telephone only, (2) users of cell phone only, (3) dual users who use landline mainly, and
(4) dual users who use cell phone mainly.
For the landline interviews, households will be selected using a random-digit-dialing (RDD)
procedure by employing GENESYS, a database-assisted sampling methodology. The GENESYS
system uses a database of working residential telephone banks for the entire United States to
produce a single-stage random sample of residential telephone numbers. RDD samples from the
GENESYS system eliminate the reduction in precision caused by the multi-stage cluster designs of
traditional RDD procedures. GENESYS samples are widely accepted because of their
methodological rigor and efficiency.
The GENESYS database is constructed from three sources: a master list of area code-exchange
combinations obtained from BELLCORE, a summary file of listed telephone numbers in the United
States obtained from Donnelly, and a summary file obtained from CATI and other sources that
cross-references zip codes to telephone exchanges. The telephone numbers in these sources are
matched and analyzed to produce a database of two-digit banks that contain at least 99 percent of
the eligible telephone numbers in the U.S. (A two-digit bank consists of the first eight digits of a
10-digit telephone number within which up to 100 telephone numbers could be assigned, e.g.
123/456-78xx). The database is used to generate a random sample in which every telephone
number, whether listed or not, has an equal probability of selection. The sample, unlike a
traditional RDD sample, has no design effect associated with clustering of telephone numbers
within telephone exchanges.
Identification of the designated respondent (DR) will be achieved by the most recent birthday
method. Once household eligibility has been established, interviewers will ask to speak with the
adult household member who had the most recent birthday. The DR will be selected prior to any
questions about at-home status or availability of potential DR, and no substitutions will be allowed.
If the DR will be unavailable throughout the study period, the household will become ineligible.

The survey will over-sample African-American and Hispanic populations by dividing the landline
telephone exchanges into three strata: a stratum of geographic areas with high concentrations of
African-American population, a stratum of geographic areas with high concentrations of Hispanic
population, and a stratum with the remainder of the U.S. The first two strata will be sampled with
higher rates. These sampling rates will be determined to achieve the desired numbers of AfricanAmerican and Hispanics based on estimated incidences within each stratum. The final sample
numbers for Hispanic and African-Americans will occur at random from the sample without
screening. The geographic areas with higher African-American and Hispanic concentrations will be
identified using GENESYS. In addition to the landline telephone exchanges, we may also
oversample cell phone users because research indicates that proportionately more AfricanAmericans and Hispanics are cell phone users than other racial groups.
2.

Procedures for the Collection of Information

The survey will be conducted by a contractor using computer-assisted telephone interviewing
(CATI) technology. Each landline interview will consist of two parts: the household screener and
the survey questions. The household screener will be used to locate eligible households and to
identify a designated respondent (DR) as described below. Only one respondent per household will
be interviewed. Each cell phone interview will only include the survey questions and will not
include any within-household eligibility screening.
Information will be collected by experienced and specifically trained telephone interviewers.
Quality control will be assured by periodic monitoring of on-going interviews throughout the study.
This monitoring replaces the previously used validation interview, which required maintaining the
name and telephone number of the respondent until the validation interview could be completed.
3. Methods to Maximize Response Rates and Deal with Non-response
In an effort to increase response rate, we plan to take the following measures:
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send advance letters to those households whose addresses can be found to notify them
the impending interview;
make as many call attempts as needed, up to 30 call attempts for a landline number and 5
call attempts for a cell phone number, to complete an interview;
keep the length of the survey to an average of 15 minutes;
allow a field period of 120 days;
stagger calling in various times of the day and days of the week;
send conversion letters to those who initially refuse the interview and use conversion
specialists to conduct conversion calls;
use a Spanish questionnaire to accommodate respondents who do not speak English;
conduct a non-response study to identify potential non-response biases and adjust
estimates statistically, if necessary; and
regular and continuous monitoring of interviewer performance and address any
operational issues in a timely manner.
non-responders for whom an address match is available in advance of the conversion
attempt.

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4.

Test of Procedures or Methods to be Undertaken

Two types of tests of the collection procedure are planned to minimize collection burden on
respondents and improve quality of collected information.
We plan to conduct 18 cognitive interviews. The primary purpose of these interviews is to
understand the mental processes that respondents use to answer survey questions. We will use
cognitive interview findings to revise the draft questionnaire, if necessary and appropriate.
The second type of tests is field pretests focusing more on the length of the questionnaire and
respondent burden in an environment as close as possible to the real interviews. The data collection
contractor will administer the full instrument by telephone to 200 randomly-selected adults shortly
before OMB approval of the collection of information is expected. Scheduling the pretests close to
the beginning of data collection will gain efficiency by using interviewer training for both the
pretests and the complete data collection. The pretests will also serve the purposes of addressing
problems in respondent selection, interviewer instructions, skip patterns, and design of the
computer-assisted-telephone-interview program.
5.

Individuals Consulted on Statistical Aspects and Individuals Collecting and/or
Analyzing Data

A contractor will collect the information on behalf of the FDA. The contractor will be tasked to
provide statistical consultation to the survey. Analysis of the information will be conducted
primarily by staff on the Consumer Studies Team, Center for Food Safety and Applied Nutrition,
FDA.

Reference:
American Association for Public Opinion Research (AAPOR). 2010. New Considerations for
Survey Researchers When Planning and Conducting RDD Telephone Surveys in the U.S. With
Respondents Reached via Cell Phone Numbers. Available at
http://www.aapor.org/Cell_Phone_Task_Force_Report.htm.

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