Definition:  Measurement that occurs when the participant is unaware of being observed.

          Description.  Webb et al. (1981) described four types of unobtrusive measurement:  Archival records, observation in contrived settings, physical traces, and simple observation.  Archival records refers to stored information typically put to a use for which the data were not originally intended (e.g., school records used in a research study).  Observation in contrived settings indicates that an observer collects data in a setting, such as a laboratory, established by the researcher for unobtrusive observation; alcohol researchers, for example, have set up simulated bars to observe participants’ drinking under varied conditions. Physical traces are artifacts left by persons (in garbage, for example) indicative of some activity or characteristic. Simple observation (described in an earlier section) indicates that an observer watches and records behaviors of interest to the observer.  In all cases, such data collection occurs without the awareness of the participant, thereby decreasing problems with reactivity, the tendency for individuals to change their behavior when they are aware of being observed.  A video description of unobtrusive measurement can be found here.

Four important problems accompany many attempts at unobtrusive measurements (Kazdin, 1992).  First, the behavior of individuals in naturalistic or contrived situations, for example, is unlikely to be a direct reflection of a single construct.  Alcohol consumption in a bar, for example, will be influenced by one’s physiological and psychological states as well as the social context. Second, researchers must expend considerable effort to obtain an unobtrusive measurement; administering a self-report scale to alcohol treatment participants is much easier than creating a simulated bar or observing individuals drink on weekend nights at an actual restaurant or bar.  Third, collecting unobtrusive measurements without arousing participants’ suspicions may be difficult; in such situations (e.g., a simulated bar), participants are likely to be guessing at experimenters’ hypotheses.  Fourth, ethical questions are frequently raised with unobtrusive measurement; any type of direct or indirect deception requires substantial justification, particularly with Institutional Review Boards.

For an expanded description of unobtrusive measurement, read about types and this summary.