ago, one of the authors began his career in marketing
and opinion research as an in-person interviewer in
Scotland. After he completed his very first interview,
the elderly Scottish woman respondent looked at him
with a twinkle in her eye and asked, "Och, you don't
believe all the things the folks tell you, do you?"
All too often, of course, we do. This credulity, this
tendency to believe answers respondents give us, may
be one of the most serious weaknesses in survey research.
And not worrying about it makes our lives easier and
When asked by skeptics whether respondents
might lie to us, we point to the generally accurate
record of opinion polls as "proof" that most people
don't. And yet we have always known that when there
is a socially desirable response-such as not beating
your wife-the corresponding undesirable behavior or
belief is sometimes underreported.
Over the past few years
the authors have been involved in hundreds of surveys
both online and by telephone, and we began to notice
sizable differences between the two methods in the replies
to questions like this which did not appear to be sampling
errors. One dramatic example of this occurred with
a question about sexual orientation. When we asked this
near the end of fifteen-or twenty-minute telephone
surveys with randomly selected samples (not a panel),
we consistently found that 2 percent of all adults identified
themselves, in their verbal replies to human interviewers, as "lesbian, gay, bisexual, or transsexual."
When we asked the identical question near the end of
fifteen-minute online surveys of samples of adults drawn
from our multimillion-member Harris
Poll Online Panel of respondents (who had opted
into our panel to do surveys), we consistently found
6 percent (or occasionally 5 percent or 7 percent) who
self-identified as lesbian, gay, bisexual, or transsexual
(LGBT). This difference was found in parallel surveys
where, even after weighting
to compensate for sample differences, the responses
to most other questions were almost identical.
One question we
considered when we compared these responses (6 percent
versus 2 percent LGBT) was whether the samples were
different-that is, even after weighting, could there
be a sampling difference and not a method
effect? Somehow it seemed implausible that people
who were lesbian, gay, bisexual, or transsexual were
three times more likely to volunteer to join our panel
than those who were not. We concluded that this was
probably a classic case of social desirability bias.
But, if so, we would expect to find similar differences
in the replies to other items on the survey. This prompted
several obvious questions:
- Was the difference a result of many
people's reluctance to "admit" to their sexual orientation
to a live human interviewer, and their much greater
willingness to do so in online surveys with a survey
organization they trusted enough to voluntarily join
its panel of willing respondents?
- Were these differences produced
by a method effect (as opposed to being sampling differences)?
- Did these differences affect a much
broader set of questions than just sexual orientation,
and if so, what types of questions?
- Do our telephone surveys have a
larger social desirability bias than our online surveys?
(We say "our" because the differences may not apply
to all telephone or all online surveys.)
To address these questions,
Harris Interactive added a set of identical questions
to two nationwide omnibus surveys conducted in the United
States in October 2003. One was a telephone survey of
1,017 adults surveyed between October 14 and 19, 2003.
The other was an online survey of 2,056 adults surveyed
between October 21 and 27. Of the 2,056 respondents
in the online sample, 526 were randomly assigned to
be asked a battery of yes
or no questions on whether they engaged in certain
behaviors or held certain beliefs. All respondents in
the telephone survey were also asked about these. Another
486 in the online sample were asked to rate
the behaviors and beliefs according to the degree
to which they considered them good or bad, in order
to establish the level of social desirability for each
item. Both surveys were weighted by the same demographic
variables (sex, age, education, race/ethnicity, number
of adults in household). The online sample was also
weighted using "propensity
score adjustment" to compensate for other biases
in our online surveys.