Usefulness

Like many of the issues and key terms in psychology, we know the gist of this term but it's one that is pretty hard to answer in an exam situation. What does it mean, and what points can we make on usefulness?

Usefulness refers to whether a piece of research or a theory is useful, practical or applicable. A useful piece of research is one that can be accurately generalised to a wide population or the target population and benefit a number of people or causes.

Accurately generalised to a wide population. You can actually split this definition pretty cleanly into three evaluative points: internal validity, external validity (including population and ecological) and to what extent it takes a nomothetic approach. 

Internal validity
It encompasses a number of individual factors, and you'll have to really think about it in terms of the question to know what part is relevant to evaluate. Most of the time, it's either face validity (is it measuring what it intends to measure?) or construct validity (is the definition in the research actually accurate? Often a problem with stress is that it's hard to define stress, and often it's operationalised in a way that isn't truly accurate). If either are poor, a study isn't going to be very useful.

External validity
There are three main types: ecological validity (conducted in a real-life situation, i.e. has mundane realism), population validity (representative, large sample) and temporal validity (whether the research is only really applicable at one time). If any of these are poor, it's not going to be as useful as we would ideally like.

Nomothetic
Nomothetic in psychology refers to a theory which can be assumed to be a general law or principle of behaviour. If it is, it's more likely to be useful. The more "exceptions to the rule" there are, the less it's going to be useful. For example, Loftus et al's theory about weapon focus is pretty nomothetic, as is the theory about hassles causing more stress than life events. Findings from research that aren't nomothetic and can only be applied to a small number of people or situations aren't very useful.