So far in my budding career I've been involved in three psychology studies, all of which required the recruitment of non-clinical participants. Even before that, my psych undergraduate final-year project on schizophrenia was carried out by surveying non-clinical participants. For the benefit of lay readers, non-clinical participants refers to "normal" people who are recruited to take part in the study and are different to results gleaned from sufferers of psychosis, anxiety or other conditions which happen to be under the experimental purview, and who are generally termed as "clinical participants". The usual trend in studies like these are to compare the results of "normal" versus "abnormal" people to an experimental condition, in order to compare any differences between the two groups and statistically interpret them to arrive at conclusions. Non-clinicals popularly consist of family, friends, even complete strangers (those willing to take part in your study anyway!). Another popular recruitment strategy is through local (or even national) newspapers, community notices, bulletin boards, and so on.
Given this background, a recent item in the British Psychological Society Research Digest caught my eye, an item to do with the assumption of mental health among non-clinical participants. You see, if you want to compare the results between "normal" and "abnormal" people, you had better make sure that the two groups are representative! In other words it would be fair to presume that the "normals" are of sound mental health, but a recent experimental study by Thurston et al. (2008) suggests that quite a substantial number of them have their own psychiatric problems, some of whom were receiving therapy. This would mean that non-clinical participants are perhaps not that representative after all!
The gist of the study is something like this: 224 families were assessed after being recruited through newspaper advertisements mainly in South-Eastern USA, and found that 11% of the teenagers, 20% of the mothers, and 13% of the fathers met the diagnostic criteria for one or more psychiatric disorders. On therapy concerns, the chips fell so that 12% of the teenagers, 20% of the mothers and 11% of the fathers were receiving it.
What this all means is that the validity of studies comes under question. When studies are carried out in comparing performances or responses of clinical and non-clinical participants, how valid can they be when there is a reasonable chance that the non-clinical participants have mental health issues? It certainly casts a new light on things. I wouldn't go as far to call every such study into question, but it perhaps gives cause to re-evaluate studies that reported a finding of some controversy. However, Thurston's team suggested that differences identified in previous studies between clinical and non-clinical groups may have been down to a factor other than the clinical status of the two. Variances may be good for something after all as any psych statistician could verify.
In terms of recommendations, Thurston's team suggest that screening of participants should take place. Hmmmm, I think this might be a tad too much on the time-consuming side. Taking the time and costs involved in running a typical study into account, is it feasible to screen participants with procedures apart from the usual demographic details that ascertain suitability for the study in the first place? And what exactly would screening involve? Administration of the BAI and/or BDI-II scales, with the Rosenberg Self-Esteem Scale thrown in for good measure? Again, it does seem a lot of time and effort to spend. One of the studies I'm associated with at the moment involves the administration of these measures and more, but only because various measures of mood are essential to the study. How ironic this all is, when clinical participants are relatively easy to acquire and it looks like considerable energy is to be expended in ensuring that non-clinicals are the right kind of non-clinicals!
Indeed, Thurston et al. say they have no "perfect answer" as to whether objectionable non-clinicals ought to be removed from studies, but that it is the responsibility of the researcher to weigh the costs and benefits of any exclusionary criteria for a particular study. Hmph, that sounds about right.
Idia B. Thurston, Jessica Curley, Sherecce Fields, Dimitra Kamboukos, Ariz Rojas, Vicky Phares (2008). How nonclinical are community samples? Journal of Community Psychology, 36 (4), 411-420 DOI: 10.1002/jcop.20223