Psychopathology among persons responding to participation as normal controls in behavioral research studies☆☆☆★

Methods 

Results 

Inquiries (N = 3,289) were made for the behavioral research subject positions. Of the inquiries, 1,689 were Caucasian, 942 African American, 467 Hispanic, 91 Asian, and 100 other; there were 1,875 men and 1,414 women; and the mean age was 28 ± 8 years. The number of exclusions by telephone, in-person screening, and medical screening are listed in Table 1.

Table 1. Number of Exclusions by Telephone, In-Person, and Medical Screening

		Telephone	In-Person	After Evaluation
	Total no. of subjects screened	3,289	1,045	455
	Uninterested/unavailable	762	173	6
	No-show for evaluation/study	-	130	9
	DSM-III-R diagnosis	581	176	5
	Psychoactive substance use	289	95	2
	Mood disorder	123	31	0
	Personality disorder	89	35	3
	Schizophrenia	33	2	0
	Anxiety disorder	44	12	0
	Eating disorder	3	1	0
	Neurological history	533	111	4
	Low priority	368	-	-
	Accepted for evaluation	1,045	455	431

Thirty-two percent (n = 1,045) were subsequently evaluated in person. After the in-person evaluation, 16% met the criteria for a DSM-III-R diagnosis, including psychoactive substance abuse (9%), mood disorder (3%), personality disorder (3%), schizophrenia (0.1%), anxiety disorder (1%), and neurological disorder (11%). Twelve percent (n = 130) of the individuals scheduled for an in-person evaluation did not show up for their appointment and 17% (n = 173) were uninterested after receiving a more detailed explanation of the purpose, procedure, and protocol. The psychopathological characteristics of qualified nonparticipating normal controls are listed in Table 2.

Table 2. Psychopathological and Neurological Disorders of Nonparticipating and Qualified Individuals Participating as Normal Controls

		Nonparticipating	Participating
	Total no. qualified	173	455
	DSM-III-R diagnosis	7	5
	Psychoactive substance use	1	2
	Mood disorder	2	0
	Personality disorder	1	3
	Schizophrenia	0	0
	Anxiety disorder	2	0
	Eating disorder	1	0
	Neurological history	2	4

Of 2,834 excluded individuals, 79% were excluded by telephone (n = 2,244) and 21% by in-person screening (n = 590); of 1,045 applicants passing the telephone interview, 57% were excluded by in-person evaluation. A large number of volunteers (n = 533) did not qualify due to their neurological history: 16% determined by telephone screening and 11% by in-person screening. The remaining 14% (n = 455) underwent medical evaluation by a physician and 431 were accepted as normal controls in ongoing studies.

Discussion 

A high prevalence of psychopathology, neurological disorders, and past/current drug usage was found in individuals inquiring about participating as normal controls in behavioral research. As a result, only a small fraction (14%) of the total persons was enrolled. These results confirm other smaller studies, where only 9% and 23% of total individuals assessed were invited for participation as normal controls in research.1, 12 The initial screening by telephone excluded a significant proportion (79%) of individuals with psychiatric and neurological disorders, and the in-depth diagnostic psychiatric interview excluded an additional (57%) individuals who had passed the telephone interview.

Previous studies using the structured psychiatric assessment, the Structured Clinical Interview for DSM-III-R: Non-patient Version, recruited 252 of 1,284 volunteers by telephone interview and 76 of 312 interviewees by psychiatric interview.1 In another study, 7% (8 of 109) were excluded by telephone interview and 47% (23 of 49) by psychiatric evaluation.12 These results reinforce the idea that a systematic clinical assessment of normal controls should be an essential component of screening psychiatric illnesses in volunteers, and the combination of telephone and in-person screening may provide a more efficient means of screening for normal controls.

The difficulty of subject recruitment is well established. One of the problems in attaining a potential research subject may lie in the scheduled hours for recruited subjects to work. Thus, subject recruitment may want to target organizations and/or “average” working persons by scheduling studies after normal work hours or even on weekends. More subjects may also be enrolled by offering more substantial remunerative payments.1 Another area that may require more investigation is cost-effective strategies of advertising for subject solicitation.

Psychiatric history is usually not included in studies that are not directly involved in behavioral research. However, behavior analysis depends on systematic replication rather than randomization of subject selection and assignment in order to obtain generality of its results. Traditionally, subject description has been limited to routine demographic information such as age, gender, education level, and diagnostic categories. However, one of the most important pieces of information necessary for experimental replication is selection criteria of subjects, which is often not included in published reports.9 This is true despite the fact that knowledge of subject selection can affect both interpretation of results and conclusions as well as replication of studies.8 With the results of this study and previous studies displaying an increased incidence of mental illness in volunteer control subjects,1, 2, 4, 12, 13 psychiatric evaluation should be considered as an essential component of the selection process of all volunteer subjects for both biological and psychiatric studies. Many of the individuals responding to research participation solicitation may not be indicative of the general population.1, 12 Previous studies have found a higher incidence of psychopathology in volunteers than would be expected in the general population, with up to 52% of “normal healthy” volunteers having a psychiatric illness.14, 15, 16 Other studies have demonstrated a broad range of detected psychopathology from 16.5% to 65% in “normal” volunteers.3, 5, 6, 17, 18, 19, 20, 21 The use of different diagnostic procedures from the ones used in our study must be taken into account. In addition, the high prevalence of psychopathology among these individuals inquiring about participation in behavioral research studies may be explained by the increased motivation of thrill-seeking, release from inhibitions, and self-discovery of volunteering compared to individuals who are motivated by financial gain or scientific curiosity.4

This study supports the importance of more scrutiny placed in the recruitment of normal controls. Given their heterogeneity, screening normal controls may require as much rigor and standardization as screening and assessment of patients.1 In addition, inclusion and exclusion criteria need more standardization. Implementing screening of control patients with telephone and in-person screening may provide for a more effective way to include normal subjects in behavioral research. It is clear from the present study and past research that further studies are warranted to investigate the process by which controls are selected.1, 2