| Summary: | Abstract Background The process of assessing the decision-making capacity of potential subjects before their inclusion in clinical trials is a legal requirement and a moral obligation, as it is essential for respecting their autonomy. This issue is especially important in psychiatry patients (such as those diagnosed with schizophrenia). The primary purpose of this article was to evaluate the degree of impairment in each dimension of decision-making capacity in schizophrenia patients compared to non-mentally-ill controls, as quantified by the (MacCAT-CR) instrument. Secondary objectives were (1) to see whether enhanced consent forms are associated with a significant increase in decision-making capacity in schizophrenia patients, and (2) if decision-making capacity in schizophrenia subjects is dependent on the age, gender, or the inpatient status of the subjects. Methods We systematically reviewed the results obtained from three databases: ISI Web of Science, Pubmed, Scopus. Each database was scrutinised using the following keywords: “MacCAT-CR + schizophrenia”, “decision-making capacity + schizophrenia”, and “informed consent + schizophrenia.” Results We included 13 studies in the analysis. The effect size between the schizophrenia and the control group was significant, with a difference in means of −4.43 (−5.76; −3.1, p < 0.001) for understanding, −1.17 (−1.49, −0.84, p < 0.001) for appreciation, −1.29 (−1.79, −0.79, p < 0.001) for reasoning, and −0.05 (−0.9, −0.01, p = 0.022) for expressing a choice. Conclusions Even if schizophrenia patients have a significantly decreased decision-making capacity compared to non-mentally-ill controls, they should be considered as competent unless very severe changes are identifiable during clinical examination. Enhanced informed consent forms decrease the differences between schizophrenia patients and non-mentally-ill controls (except for the reasoning dimension) and should be used whenever the investigators want to include more ill patients in their clinical trials. Increased age, men gender and an increased percentage of inpatients might increase the differential of decision-making incompetence compared to non-mentally-ill subjects in various dimensions of the decision-making competence as analysed by the MacCAT-CR scale, but the small number of subjects did not allow us (except for one instance) to reach statistical significance.
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