113 6 DELIRIUM | PART THREE validity of the DOS were tested in two prospective studies in high risk groups: geriatric medicine patients and elderly hip fracture patients [18]. The DOS has high internal consistency (0.96) and high content validity (α = 0.93). In these study groups the DOS scale had a sensitivity of 89-100% and a specificity of 68-88%. The positive predictive value was 47%, the negative predictive value was almost 100%. The DOS was also able to measure severity of delirium in geriatric patients [24]. Moreover, the DOS proved to be a good instrument to facilitate early recognition of delirium in patients who undergo cardiac surgery: the sensitivity and specificity of the DOS was 100% and 96.6% respectively [25]. DRS-R-98 The DRS-R-98 is a revised version of the Delirium Rating Scale [26, 27]. The DRS-R-98 consists of 13 severity items that are scored from 0 (not present) to 3 points (severely present), and three diagnostic items, all of which are rated over the past 24 hours. Severity scores range from 0 to 39, and total scores range from 0 to 46. The DRS-R-98 is designed to be completed by a trained professional and takes about 10 to 15 minutes to complete [27]. The DRS-R-98 has a high internal consistency (0.90) and when using a cut-off of 17.75 points on the total scale a sensitivity of 92% and specificity of 95% [27]. Inter-rater-consistency was high in the validation study by Trzepacz et al (0.99) [27]. The DRS-R-98 severity scale has the great benefit that it can be used for repeated measurements to assess the response to delirium treatment [27]. Recently, the DRS-R-98 has been validated for the new DSM-5 criteria [28]. The DRS-R-98 was chosen as the gold standard to evaluate the accuracy of the DOS because of its good psychometric qualities, because it has been validated in a palliative care setting, and is available in the Dutch language (the first language of the included patients and the researchers in this study group) [27]. Statistics A sample size calculation was conducted to determine an 80% power in demonstrating that the DOS has a sensitivity of at least 90%. A sample of 100 patients per group (DOS positive vs. DOS negative) was needed when the sensitivity of the DOS was assumed to be 95% [18, 25]. Primary endpoints to assess the accuracy of theDOS are the sensitivity and specificity of the DOSscorecomparedwiththeDRS-R-98as thegoldstandard. Sensitivity, specificity, negative and positive predictive value are reported with 95% confidence intervals, calculated with the Wilson method [29]. Analyses will be corrected for partial verification, because only a proportion of DOS negative patients admitted to the study sites were included in this study. For the baseline characteristics standard descriptive statistics were used. Statistical analyses were performed with IBM SPSS version 22.0 (IBM, Armonk, NY, USA). Results Between January 2010 and January 2016, 100 consecutive DOS negative and 95 DOS positive patients were included in the study. One DOS positive patient withdrew consent
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