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Food Safety Survey
OMB Control No.
0910-0345—Reinstatement
SUPPORTING STATEMENT
B. Statistical Methods (used for collection of information
employing statistical methods)
1. Participant Universe and Sampling Methods
Unlike
previous Food Safety Surveys that only used a single sampling frame
of all telephone households in the United Sates, this wave of the
survey will use a dual-frame (Landline and Cell phone) sampling plan.
The plan calls for a landline household sample of 2,400 participants
and an additional sample of 1,600 participants from cell phones. One
half of the landline sample (1,200) and the cell sample (800) will be
randomly assigned to one of the two survey versions. Each frame is
explained below.
Landline
frame:
The
participant universe for this survey is all landline telephone
households in the United States. Eligible households are defined as
those containing one or more adults who have the following
characteristics: aged 18 years or older, speak English or Spanish,
sufficiently good health for a telephone interview.
Similar
to all previous Food Safety Surveys, households will be selected
using a Random Digit Dialing (RDD) procedure by employing GENESYS, a
database-assisted sampling system. 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.
Cell Phone Sample Frame:
The
participant universe for this survey is all cell phones in the United
States. Eligible participants are defined as: aged 18 years or
older, speak English or Spanish, sufficiently good health for a
telephone interview.
The
cell phone sample frame will be supplied by MSG. MSG provides a
comprehensive sampling frame for the selection of cellular RDD
samples. Wireless frame construction begins with the most recent
monthly Telcordia Terminating Point Master (TPM) data file.
Telcordia Technologies is the leading provider of software, database,
and services for the Telecommunications Industry. They offer a
variety of products and services including ones that MSG licenses for
the construction of its sampling-based products and databases.
Specifically, MSG uses Telcordia products for the identification of
wire line, VoIP, and wireless thousand series blocks that are used in
the creation of the wire line and wireless RDD databases. The TPM is
Telcordia’s master file of NPA-NXX and Block-ID records for the
North American Number Plan. It contains at least one record per
NPA-NXX. For prefixes NPA-NXXs, where 1000-block number pooling is in
effect, this file also provides information for individual
1000-blocks. This allows users to identify those 1000-blocks that
have either not been assigned for service or that have been allocated
to different service providers.
Selection
of wireless prefixes and blocks occurs by selecting all records where
the NXXTYPE is dedicated to cellular devices, shared “plain old
telephone service” (POTS) and cellular, PCS, shared POTS and
PCS, paging (in mixed or shared blocks), mobile, and miscellaneous.
Using the TPM file as a source, all 1000-series telephone blocks
dedicated to cellular devices are isolated. From the identified 1000
series telephone blocks dedicated to cellular devices, MSG generates
a random sample of possible telephone numbers. New
exchanges/1000-blocks are included in the frame. They have an
activation date on or before the release date associated with the
release date of the wireless frame.
Exchange
records for which there were no 1000-block records are expanded to
ten (10) 1000-block records. This file is then further expanded to a
file of 1000-blocks, 10 100-block records per 1000-blocks containing
the same information as the 1000-block record. “Mixed”
or “shared” 100-blocks are then compared to MSG’s
list-assisted RDD database. 100-blocks with no listed numbers are
retained in the wireless frame and 100-blocks containing listed
numbers on the RDD frame are removed. The result is a frame of
100-blocks that is mutually exclusive of MSG’s list-assisted
RDD frame while allowing coverage in prefixes and 1000-blocks that
potentially provide both landline and wireless service.
At
this point, the frame size has been fixed and divided into
equal-sized subsets of ten-digit numbers. Within each of the
subsets, one number is selected at random giving all numbers an equal
probability of selection.
The
sampling interval is calculated by dividing the universe of all
possible numbers by the number of records desired, thus specifying
the size of the frame subdivisions. The file of 100-blocks is sorted
by FIPS Code, Carrier name, and 100-block. The intent is to provide a
stratification that will yield a sample that is representative both
geographically and by large and small carrier. A sampling interval is
determined by dividing the universe of eligible 100-blocks by the
desired sample size. From a random start within the first sampling
interval, a systematic nth selection of 100-blocks is performed and a
2-digit random number between 00 and 99 is appended to each selected
100-block stem.
An
Operating Company Number (OCN) for the 1000-block is retained on each
record. The Carrier Name has been attached to each record based on a
Telcordia table of OCN codes and names. Carrier Names and codes
(OCN) frequently do not reflect mergers and acquisitions. These
acquisitions may be national in scope or state specific. For
example, Southwestern Bell Wireless and parts of Pacific Bell
Wireless were bought by Cingular but still reflect the original
carrier name and OCN. Carrier Names and codes are frequently
different by state, particularly for large wireless companies
offering national or almost national service. These companies also
frequently distinguish different corporate entities between their
landline, cellular, and paging divisions. Therefore a unique OCN will
not always represent a unique carrier and vice versa. The carrier
identification is for the 1000- block and will be inaccurate for
subscribers who have ported their cell phone number to a different
cellular provider.
Screening
for disconnects is not available for wireless sample since it would
violate Telephone Consumer Protection Act of 1991 rules prohibiting
dialing wireless numbers using automated telephone systems. Landline
numbers that have been ported to wireless service will not be
included since they are on the RDD frame, unless they are wireless
numbers that have been ported to landline service.
Sampling:
The
survey will oversample Hispanics and African-Americans. The target
number of Hispanics and African-American is, 400 or 10% each out of
4,000 interviews. The 2010 US population percentages of
African-American and Hispanic Americans are approximately 13.6 and
16.3 percent, respectively. Practically, these groups are less
likely to be contacted and to cooperate in landline segment surveys.
As a result, the sampling plan will over-sample these population
groups.
Tied
to the sample design is the construction of the sampling weights.
The FSS study includes two frames – the frame for both landline
households and the cell phone frame. The landline frame consists of
the area codes and exchanges for landline phones. The cell phone
frame consists of the area codes and exchanges dedicated to cell
phones.
Post-stratified
adjustment will be made for age, gender, education, and
race/ethnicity.
A
sample size of 4,000 is needed to adequately perform all of the
sub-analyses that are needed for the proposed Healthy People 2020
objective relating to consumer practices. This objective requires
that we look at disparities in safe food handling habits among
different populations. Some of these sub-analyses of interest
include showing change over time for: Blacks or African-Americans,
older adults (60+), and households with young children (<5 years
old). A power analysis was conducted to determine the sample size
needed to analyze changes in these sub-groups.
Identification
of the designated participant will be achieved by using the last
birthday method for the landline survey. Once household eligibility
(for landlines) has been established, interviewers will ask the
person who answers the phone to speak with the adult age 18 and over
in the household has had the most recent birthday. This method has
been used for all five waves of the Food Safety Survey.
Unlike
landlines, cell phones are generally individual devices, so the
person who answered the phone is likely to be the only eligible user
of the phone. However, there are some cases of shared user cell
phones. In the screening questionnaire we will ask the participant
if the cell phone we just dialed is shared with anyone else in their
household. If the response is “yes,” we will follow the
same “most recent birthday” approach described above for
landline participant selection. We will make sure the participant is
at least 18 years old prior to conducting the interview.
Procedures for the Collection of Information
The
Food Safety Survey will be conducted using computer-assisted
telephone Interviewing (CATI) technology. The interview will consist
of two parts: the screener and the extended interview (Attachment A).
The screener will be used to locate eligible households (landline)
and to identify a qualified participant as described in section B.1
above. Only one participant per household will be interviewed.
Data
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.
Methods to Maximize Response Rates and Deal with Non-response
To help ensure that the response rate is as high as possible, the
Contractor will employ all appropriate methods demonstrated in the
research literature on survey methodology. These procedures include
the following:
Design a questionnaire that
minimizes participant burden (short in length, written in
easy-to-understand language).
Test the draft questionnaire
using cognitive interviews to ensure that participants can properly
understand the questions and that the response options are robust.
Test the draft questionnaire in
a pre-test to ensure that it is working as expected.
After the landline sample is
drawn, all households for which an address can be matched to the
telephone number will be sent a letter letting them know that they
have been selected to participate in the survey (Attachment B).
In addition to general
training, all interviewers and supervisors will be trained on the
specifics of the survey by a member of the project's professional
staff. This will include an explanation of the importance and
purpose of the survey, as well as a thorough review and practice
reading of the entire survey instrument.
A reasonable number of call attempts will be made to determine
whether an "initial contact"—the establishment of
the identity of a telephone number (residential or
non-residential)—is made. For example, if the first
three attempts received no response and the fourth attempt received
a busy signal, the number will be called for a few more times to try
to make an initial contact because the fourth attempt suggests this
number has the potential of being a residential number. Only
when there is certainty that a number is not a residential number
will the limit of five attempts be applied. If a voicemail or
answering machine indicates the number is residential, then an
initial contact is considered made.
No-answers after these attempts at initial contact will be regarded
as non-households and eliminated from the sample. Households that
initially refuse to participate will be sent a letter acknowledging
the initial contact and asking again for the household’s
participation. Addresses will be obtained through a commercial list
of known telephone number/address combinations. The letter will
identify FDA as the sponsor of the survey, give a brief explanation
of the study topic, and stress the importance of participation.
Refusal conversion calls will be scheduled several days after the
letters are sent out, in order to give the letter ample time to
arrive, but close enough to the arrival date to be remembered by the
participant (Attachment C).
When possible, screening and extended interviews with designated
participants will be completed during the same call. If the
participant is not available at the time of the screening call,
additional callbacks will be made in an effort to complete the
interview. Participants who are not reached will be included in the
denominator for the calculation of the response rate. Participants
who initially refused will be sent a letter encouraging
participation if an address match can be made.
To determine if there are any systematic differences between those
who participate in the FSS and non-responders, FDA will conduct a
non-response analysis. Fifty initial refusals (i.e.,
non-participants) who have refused to participate twice; once when
first called and a second time when called back, will be asked to
take a shortened questionnaire consisting of core questions and a
subset of the demographic questions (Attachment D).
4. Test of Procedures or Methods to be Undertaken
FDA plans to perform two tests to minimize collection burden on
participants and improve quality of collected information. The first
test consists of cognitive interviews; the primary purpose of these
interviews is to understand the thinking processes that participants
use to answer the survey questions. Nine (9) cognitive interviews
will be conducted to refine the survey questionnaire.
The Food Safety Survey will be pre-tested with up to 18 participants
shortly after OMB approval of the information collection is expected.
Scheduling the pretest close to the beginning of data collection
will gain efficiency by using interviewer training for both the
pretest and the complete data collection. Because the survey is
based largely on questions from the previous surveys, 18 pretests
should be adequate to estimate the time required to complete the
interview, to assure clarity of the added or changed instructions,
questions, and response categories, and to check the CATI programming
for correct skips and other procedures.
Representatives of FDA and the contractor will monitor the pretest
interviews. Few changes to the questionnaire are expected from the
pre-test, because we want to compare responses with identical
questions asked on previous surveys. OMB will be provided with
copies of the final questionnaires prior to implementation of the
study.
Individuals Consulted on Statistical Aspects and Individuals
Collecting and/or Analyzing Data
The contractor, IPSOS, will collect the information on behalf of FDA
as a task order under the Quick Turn Around Survey Data Collection
contract. Dr. Alan Roshwalb is the Project Leader for IPSOS. Data
analysis and dissemination will be led by Amy Lando, MPP, Consumer
Science Specialist at FDA, telephone 240-402-1996.
| File Type | application/msword |
| Author | alando |
| Last Modified By | Bean, Domini |
| File Modified | 2014-11-17 |
| File Created | 2014-11-17 |