Brief CommunicationExamination of volunteer bias in research involving patients diagnosed with psychogenic nonepileptic seizures
Introduction
The personality characteristics and mood features associated with psychogenic nonepileptic seizures (PNES) have been related to lower quality of life (QOL) when compared with patients diagnosed with ES [1], [2], [3], [4]. Presumably, a better understanding of the personality and mood features associated with PNES would inform clinicians of the most targeted efficacious treatments that might help reduce the symptoms of this disorder as well as underlying psychopathologies. Although progress in the diagnosis and treatment of PNES has been made recently [5], the same personality and mood features associated with this disorder are potentially related to problems determining appropriate treatments. There is a growing awareness that controlled trials are needed to determine the best interventions for treating this challenging patient population [6]. Before the results of these studies can be put into practice, however, the external validity of these findings must be established. One threat to external validity that has not been addressed within this patient population is volunteer bias (LaFrance, personal communication, 12 April 2006).
Volunteer bias is considered a threat to validity and occurs when those who participate in a study differ from those who do not [7]. Epidemiological studies examining mental illness, health care utilization, and disability have identified a number of factors that contribute to participation or nonparticipation in research. For example, socioeconomic status [8], marital status [9], and presence of psychiatric disorders [10] have been shown to be related to nonparticipation in survey research. Greater rates of nonparticipation have also been associated with younger age and male gender [11], [12]. In psychological research, studies have demonstrated that personality variables, including agreeableness and openness to experience, significantly correlate with willingness to participate in research [13]. There is also some evidence from previous work with patients diagnosed with PNES that volunteer bias may exist. In one study of 53 patients diagnosed with PNES who were contacted after receiving their diagnosis and asked to participate in a telephone survey, only 23 agreed to participate [14]. Other studies have also suggested low participation rates for patients with PNES [15], [16], but there is a paucity of research that systematically examines this methodological issue [17].
In the process of gathering data for a separate study examining personality and emotional predictors of QOL involving patients admitted to our epilepsy monitoring unit (EMU) for video/EEG monitoring, we were concerned that patients diagnosed with PNES would decline participation at a greater rate than patients diagnosed with ES [14], [15], [16], [17]. We undertook this study to determine the potential contribution of volunteer bias in patients admitted for video/EEG monitoring and who are approached for participation in research. The specific aim was to document and compare the frequency with which patients diagnosed with PNES or ES participate in personality and QOL research.
Section snippets
Methods
This study was approved by the University of California, San Francisco, (UCSF) Committee on Human Research. Patients who were consecutively admitted to the EMU from January 2006 to January 2007 were considered for participation in a study examining personality and emotional predictors of QOL. For the QOL study, patients who were under 18 years of age, too cognitively impaired to complete research protocols independently, or unable to read at a sixth grade level were excluded and, therefore, not
Results
One hundred-thirty nine patients admitted to the EMU for video/EEG monitoring met inclusion criteria and were approached for participation in the QOL study. Patients with no confirmed diagnosis of PNES or ES, patients with both PNES and ES, and patients with neither disorder (e.g., migraine) were not included in any further analysis (n = 16). The demographic characteristics of patients with a confirmed diagnosis of PNES or ES are summarized in Table 1. There were no differences in gender or years
Discussion
Methodological problems such as volunteer bias can compromise the interpretation and limit the generalizability of clinical research findings. Because previous research has suggested that patients diagnosed with PNES may decline participation in research [14], [15], [16], [17], we were concerned that these patients may have been refusing to participate in our study examining personality and emotional predictors of QOL at a higher rate than patients diagnosed with ES. Such a finding could
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