Measuring motivation in people with schizophrenia
Introduction
Motivational deficits are a prevalent feature of schizophrenia, even in the early stages of illness (Lyne et al., 2012, Fervaha et al., 2015). The importance of these symptoms is highlighted by consistent findings from several studies demonstrating that these impairments represent a critical link to the poor functional outcomes characterizing this illness (Faerden et al., 2009, Foussias et al., 2011, Konstantakopoulos et al., 2011, Green et al., 2012, Fervaha et al., 2013, Rocca et al., 2014, Fervaha et al., 2015). While several instruments exist to evaluate these symptoms, the degree of convergence between scores derived from different instruments, as well as whether motivational deficits scores overlap with ratings of symptom severity in other domains of illness (e.g., depression), is not clear.
Several ratings scales exist that evaluate negative symptoms more broadly and in doing so also tap into aspects of motivational impairment (Weiser and Garibaldi, 2015). An example of such an instrument includes the Scale for the Assessment of Negative Symptoms (SANS) which includes an avolition/apathy subscale (Andreasen, 1989). In addition to the SANS, newer negative symptom rating scales have been developed that include specific items tapping into motivational deficits (Kirkpatrick et al., 2011, Kring et al., 2013). In contrast, some investigators have utilized a motivational deficit specific instrument such as the Apathy Evaluation Scale (AES) in order to assess the severity of this domain of illness (Marin et al., 1991).
Several studies have supported the notion that motivational deficits evaluated using different ratings scales provide converging information. For example, a previous study using the newer Clinical Assessment Interview for Negative Symptoms has found moderate overlap between motivational deficit ratings derived from this scale and those derived from the SANS (Kring et al., 2013). Another study reported a high degree of overlap between motivational deficits evaluated using another new rating scale, the Brief Negative Symptom Scale, and scores derived from the AES (Hartmann et al., 2015). Motivational deficits, as rated on the SANS, have also been linked to scores from other measures of amotivation/apathy (Yazbek et al., 2014). Furthermore, in a recent study we showed that ratings of motivational deficits taken from 3 different ratings scales all provided convergent information, and factor analysis revealed a single-factor solution, suggesting that ratings from these different scales were all tapping into a similar unifying construct (i.e., motivational deficits) (Foussias et al., 2015).
In the present study we specifically examined the degree of convergence between motivational deficit scores derived from selected instruments, and further explored the discriminant validity of these scores. We hypothesized that motivational deficit scores from different instruments would be highly correlated, and would similarly not be highly related to other variables such as positive and depressive symptom severity.
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Participants
Patients with schizophrenia were recruited from outpatient clinics at the Centre for Addiction and Mental Health. Selection criteria for participants included: (1) diagnosis of a schizophrenia or schizoaffective disorder depressed subtype (no current mood episode), and an absence of any other current Axis I disorder (e.g., substance dependence within the past 3 months), confirmed using the Mini International Neuropsychiatric Interview (Sheehan et al., 1998) and medical records, (2) age 18–35
Patient characteristics
Sixty-two patients with schizophrenia participated in the present study. Sociodemographic and clinical characteristics of the sample are presented in Table 1.
Convergent validity
All of the motivational deficit scores were highly inter-correlated (Table 2). The factor analysis resulted in a Kaiser–Meyer–Olkin measure of sampling adequacy of 0.79 and a significant Bartlett's test of sphericity (χ2 = 162.0, p < 0.001). In addition, all communalities were high (i.e., greater than 0.60). Examination of the scree plot and
Discussion
The present study sought to examine the overlap in motivational deficit scores across 5 different measures, and further evaluate the relative independence of these scores from other aspects of psychopathology. We found evidence for convergent validity of the 5 scores, suggesting that each of the scores is tapping into a similar underlying construct (i.e., motivational deficits). Furthermore, with the exception of the relationship between the AES and depressive symptoms, all measures of
Funding
This work was supported, in part, by a Vanier Canada Graduate Scholarship (to G. Fervaha). This funding source had no further role in study design, statistical analysis or interpretation of findings; in writing of the manuscript; or in the decision to submit for publication.
Contributors
Fervaha and Remington designed the study and wrote the protocol. Fervaha conducted the participant assessments, statistical analyses, literature search and preparation of the first draft of the manuscript. All authors subsequently made meaningful contributions to and have approved the final manuscript.
Conflict of interest
Dr. Foussias has been involved in research sponsored by Medicure Inc., and Neurocrine Bioscience, has received consultant fees from Roche, and has received speaker fees from Roche, Lundbeck, and Novartis. Dr. Takeuchi has received fellowship grants from the Japanese Society of Clinical Neuropsychopharmacology and Astellas Foundation for Research on Metabolic Disorders; and manuscript fees from Dainippon Sumitomo Pharma. Dr. Agid has received research support from Pfizer Inc. and Janssen-Ortho,
Acknowledgments
The authors thank the participants for volunteering their time for this study.
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