Knowledge Panel

Attachment D. GfK KnowledgePanel® Recruitment and Empanelment Methodology including
Consent Recruitment Methodology

KnowledgePanel’s probability-based recruitment was originally based exclusively on a national
RDD frame. In April 2009, in response to the growing number of cellphone-only households
that are outside of the RDD frame, GfK migrated to using an ABS frame for selecting panel
members. This probability-based methodology improves population coverage. Currently,
approximately 40% of panel members were recruited through RDD, while 60% were recruited
using ABS. For both ABS and RDD recruitment, households without an Internet connection
were provided with a web-enabled device and free Internet service. After initially accepting the
invitation to join the panel, participants are asked to complete a short demographic survey (the
initial profile survey); answers to these questions allow efficient panel sampling and weighting
for surveys. Completion of the profile survey allows participants to become panel members.
These procedures were established for the RDD-recruited panel members and continued with
ABS recruited panel members. Data from respondents sampled from the RDD and ABS frames
are secure to the extent permitted by law.

ABS Recruitment. ABS involves probability-based sampling of addresses from the U.S. Postal Service’s
Delivery Sequence File. The key advantage of the ABS sample frame is that it allows sampling of almost
all U.S. households. An estimated 97% of households are “covered” in sampling nomenclature.
Regardless of household telephone status, those households can be reached and contacted through
postal mail. In late 2009 the ABS sample began incorporating a geographic stratification design. Census
blocks with high density minority communities were oversampled (Stratum 1), and the balance of the

census blocks (Stratum 2) were relatively under-sampled. The definition of high density and minority
community and the relative proportion between strata differed among specific ABS samples. In 2010,
the two strata were redefined to target high density Hispanic areas in Stratum 1 and all else in Stratum
2. In 2011, pre-identified ancillary information, rather than census block data, were used to construct
and target four strata as follows: Hispanic ages 18-24, non-Hispanic ages 18-24, Hispanic ages 25+, and
non-Hispanic ages 25+. Also in 2011, a separate sample targeting only persons ages 18-24 was fielded
across the year, again using predictive ancillary information. Combined with the four-stratum sample,
the base weight adjustment compensates for cases from this unique young adult oversample. In 2012, a
similar four-stratum design was implemented, with the ages changed to 18-29 and 30+ for both the
Hispanic and non-Hispanic strata. For every survey sample, an appropriate base weight adjustment is
applied to each relevant sample to correct for these stratified designs.

Randomly sampled addresses are invited to join KnowledgePanel through a series of mailings, including
an initial invitation letter, a reminder postcard, and a subsequent follow-up letter. Approximately 45%
of the physical addresses selected for the sample can be matched to a corresponding valid telephone
number. About 5 weeks after the initial mailing, telephone refusal-conversion calls are made to
households for whom a telephone number was matched to the sampled address. Invited households
can join the panel by:
• Completing and mailing back a paper form in a postage-paid envelope
• Calling a toll-free hotline phone number maintained by GfK
• Going to a designated GfK website and completing the recruitment form at the website

RDD Recruitment. For panel members who were recruited using RDD-based sampling (pre-April 2009),

list-assisted RDD sampling techniques were used on the sample frame consisting of the entire U.S.
residential telephone population. Only banks of telephone numbers (each consisting of 100 telephone
numbers) that had zero or one directory-listed phone numbers were excluded. Two strata were defined
using 2000 Census Decennial Census data which were appended to all telephone exchanges. The first
stratum had a higher concentration of Black and Hispanic households, and the second stratum had a
lower concentration of these groups relative to the national estimates. Telephone numbers were
selected with equal probability of selection for each number within each of the two strata, with the
higher concentration Black and Hispanic stratum being sampled at approximately twice the rate of the
other stratum. The sampling was done without replacement to ensure that numbers already fielded
would not be fielded again.

A valid postal address was recovered for about 60%-70% of all telephone numbers in the selected
samples. The telephone numbers for which an address was recovered were selected with certainty.
Until May 2007, between one-half and one-third of the remainder was subsampled randomly,
depending on the recruitment period. From May 2007 to March 2009, subsampling was done at a rate
of 75% for those households without a physical address. The households for which there was an
address-matched telephone number received an advance mailing, typically 7 to 9 days before the
recruitment telephone call. The letter informed them that they had been selected to participate in
KnowledgePanel®.

Following the advance letter, the telephone recruitment process began for all sampled phone numbers.
Cases sent to telephone interviewers were dialed for up to 90 days, with at least 10 dial attempts when
no one answered the phone and when phone numbers were known to be associated with households.
Extensive refusal conversion was also performed. Experienced interviewers conducted all recruitment

interviews. The recruitment interview, which typically required about 10 minutes, began with the
interviewer informing the household member that they had been selected to join KnowledgePanel.

Empanelment Methodology
This section covers the methods used to recruit households and invite participants to join the
KnowledgePanel.

Internet Device Provision. The first RDD recruitment to KnowledgePanel was conducted in 1999. At that
time, all households recruited were given a WebTV to use for answering surveys. In August 2002,
Knowledge Networks, Inc., acquired by GfK in 2011, began allowing households to use their own
computers connected to the Internet for taking surveys; recruited households were no longer sent a
WebTV if they reported having access to the Internet. Currently, if a household does not have a
computer and/or access to the Internet from home and subscribes to a landline phone service, the
household is given a web-enabled device (laptop or netbook) along with free monthly Internet access in
exchange for members completing a short survey on a weekly basis.

Before shipment, each web-enabled device is custom configured with individual email accounts so that
it can be used immediately by household members. Most households are able to install the hardware
without additional assistance, although GfK maintains a telephone technical support line and will, when
needed, provide on-site installation. Panel members may contact the Panel Member Support
Department for questions using a toll-free number. The Panel Member Support Department is available
Monday-Friday 9AM-12AM EST and Sat-Sun 12PM-8PM EST. The Support Department also contacts
household members who do not respond to survey invitations and attempts to restore contact and
cooperation. Panel members who have Internet access provide GfK with their email accounts and their

weekly surveys are sent to that email account.
Completion of Initial Demographic Profile Survey. Following recruitment, which includes an expressed
interest by the participant in joining the panel and providing their valid email addresses, all recruited
participants are asked to complete a follow-up survey that includes demographic questions such as
gender, age, race/ethnicity, income, education, and prior computer and Internet usage. This information
can be used for weighting as well as for determining eligibility for specific studies. This information also
eliminates the need for gathering basic demographic information on each panel survey. Once this survey
is completed, the panel member is regarded as active and ready to be sampled for other surveys.
Participants who do not complete the profile survey do not become members of the panel.

Consent. Participants consent to receive survey invitations from KnowledgePanel during the
recruitment process when respondents provide wither are asked to give their contact
information at which to receive the survey invitations. There is generally no additional consent
process for individual surveys.