Some survey researchers recognized the value of data from non-asking sources. They are to be commended! The only way to know if self-reports are correct or incorrect is to check or verify them with data from non-asking sources. Newsletter No. 97, which I received from and university survey research unit, describes how biomeasures can be used to check or verify self-reports. In bold are the parts of Newsletter No. 97 relevant to this point.
Using Survey Data in Combination with Data from Other Sources: Incorporating
Biomeasures with Survey Data
In this SNB, we consider one particular type of data that might be collected
along with survey data: biomeasures. Although surveys predominantly rely
on data from self-reports, it is increasingly common to collect other sorts of
data as well. For example, particularly in health surveys, researchers may collect biomeasures.
Biomeasures are physical measures taken by the survey interviewer
or a researcher either at the time of the survey interview or (in some
cases) at a later time during a physical exam. Examples of biomeasures collected with surveys include direct measures such as height, weight, waist/hip circumference, blood pressure; simple physical performance tests (walking, balance, strength, cognition); or collection of specimens such as saliva, urine, or blood samples.
There are several reasons why researchers may incorporate biomeasures with
survey data: 1) to make population-representative inferences, if the survey
sample is randomly drawn, 2) to serve as a reference to self-reported
behaviors and health measures, 3) to better understand causal links between social /
environmental exposures and health, and 4) to explore the role of genetics.
Biomeasures may be particularly valuable when they provide data for variables that are difficult to assess via self-report, either because respondents may not be able to accurately answer survey questions on the topic (e.g., current blood pressure) or because the questions may be sensitive (e.g., illegal drug use).
When collecting biomeasures, it is important to consider what special
training your interviewers will need in addition to standard study training, or
whether you will require special personnel. Equipment needs and laboratory
processing can greatly increase data collection costs, so it is important to build these
into the budget. Also consider how respondent cooperation to the biomeasures
will be handled in the study protocol: for instance, can respondents refuse
that portion of the study and still complete the survey? Cooperation to
biomeasures can range from very high with simple height / weight
measurements to low with something more invasive such as blood or urine samples. Some
studies build in an additional incentive for participation in the biomeasures
Giving results back to respondents is also important, whether that comes
in the form of a sheet that interviewers complete on the spot, or a formal notice
after the lab results are processed. Particularly if the biomeasures indicate
potential health concerns, researchers are ethically obligated to share their
findings with respondents.
For more information about sensitive questions, respondent cooperation/response rate, and other aspects of survey research, see The Problem with Survey Research.
See also my blog post, Counter Literature to Survey Research.