In research, an unobtrusive measure is a method of making observations without the knowledge of those being observed. Unobtrusive measures are designed to minimize a major problem in social research, which is how a subject's awareness of the research project affects behavior and distorts research results.
The main drawback, however, is that there is a very limited range of information that can be gathered this way. One way to assess the effect of racial integration in schools is to compare the academic records of students educated in schools whose student populations vary in their degree of racial heterogeneity.
Another way that one can determine the results of an experiment utilizing unobtrusive measures is to analyze data and behavior from a hidden camera or through a two-way mirror. In either case, privacy may come into play and a test subject's individual rights are in danger of being violated.
As opposed to obtrusive measures, indirect measures occur naturally during research and are available to researchers in pretty much limitless supply, depending on the researchers' innovation and imagination. Indirect measures are naturally unobtrusive and are used to collect data without introducing any formal measurement procedure of which the subject is aware.
Take for instance trying to measure foot traffic and item popularity in a fashion boutique. Although placing a person in the store to observe shoppers might give you great data on what people buy, it also has a chance of intruding on the study by letting the shopper know they were being watched. On the other hand, if a researcher installs hidden cameras and observes data collected from those to notice trend, the measure would be considered indirect or unobtrusive.
Similarly, some cell phone apps now allow retailers to track the movement of cellular devices in the store if the customer is logged into a discount app for the store. This specific geolocation can measure exactly how long customers spend in different parts of stores, without being aware they're being watched. This raw data is the closest one can get to understanding how a shopper spends his or her time in a store when he or she feels no one is watching.
Ethics and Surveillance
Unobstructive measures come with their fair share of ethics concerns, primarily in terms of privacy and surveillance. For that reason, researchers should be careful with which methods they use and how they use them when conducting these types of sociological experiments.
By definition, indirect or unobtrusive measures collect data and observations without the experiment subjects' knowledge, which could be cause for concern for this person being observed. Further, it could be a violation of the person's right to privacy by not using informed consent.
In general, it is important to understand the laws governing privacy in the context of your experiment. Chances are, most will require consent from the participants, though this is not the case with certain public spaces such as museums or amusement parks, where buying a ticket acts as a contract for the patron which often times includes video surveillance and monitoring.