[Discriminant validity and inter-rater concordance of two scoring systems for the clock test]

To compare the discriminant validity and inter-rater reliability of the two scoring systems for the Clock test that are most used in Spain.

Two collections of clock drawings obtained in a clinical context (116 cases; 56.8% women, mean age 73.1±7.7 years) and in a cohort of volunteers (2039 drawings of 579 subjects; 59.5% women, mean age 78.3±3.8 years) have been assessed. All subjects were classified as cognitively normal (CN) or cognitively impaired (CI) after extensive clinical and neuropsychological evaluation. Expert raters have evaluated these drawings independently and without knowledge of the diagnosis using the Sunderland and Solomon systems standardized in Spanish by Cacho (range 0 to 10) and del Ser (range 0 to 7) respectively. The discriminant validity of each method was calculated in the two samples using the area under the ROC curve (aROC), and the inter-rater reliability was calculated in the clinical sample, that was assessed by the two evaluators, using the intraclass correlation coefficient (ICC) and the kappa coefficient.

There are no significant differences in the discriminant validity of the Sunderland and Solomon systems in any of the samples (clinical: aROC 0.73 [CI95%: 0.64-0.81] and 0.77 [CI95%: 0.69-0.85] respectively, P=.19; volunteers: aROC 0.69 [CI95%: 0.67-0.71] and 0.72 [CI95%: 0.69-0.73] respectively, P=.08). The cut-off points ≤8 and ≤5 correctly classify 71% and 73% of the clinical sample and 82% and 84% of the volunteer sample, respectively. Both systems have good agreement in the clinical sample (Sunderland: ICC 0.90 [CI95%: 0.81-0.93], kappa 0.76 [CI95%: 0.70-0.83]; Solomon: 0.92 [CI95%: 0.88-0.95] and 0.77 [CI95%: 0.71-0.83] respectively), somewhat higher in the second, although the differences are not significant.

The discriminant validity and inter-observer reliability of these two Clock Test correction systems are similar. Solomon's method, shorter and simpler, may be more advisable in pragmatic terms.