A City Guide To Guangyuan for However, without a researcher actually being present and observing the individual behaving over long periods of time, it is difficult to know whether the behaviour a person reports to the researcher or clinician accurately reflects their actual behaviour. Obtaining valid measures of behaviour is made increasingly difficult when one is interested in behaviour that is perhaps considered undesirable’ e.g. excessive alcohol or drug use, or when it is private e.g. sexual behaviour. Researchers also face the challenge of knowing how best to define the behaviours under study, and yet it is only through appropriate definition that measurement becomes possible. A City Guide To Guangyuan 2016.