Chapter 5 122 Table 3. Results of the selection strategies. NPA FN FP TP TN PPV NPV ACC DIF Column Fig 1. n n n n n % % % % Cut-off’s I.A. n/a 290 3 209 81 400 27.9 99.3 69.4 n/a D MoCA <26 512 3 431 81 178 15.8 98.3 37.3 +77 C S.A. <21 232 3+7 158 74 451 31.9 97.8 75.8 -20 A 21<26 232 3 158 74+7^ 451 33.9 99.3 76.8 -20 B MoCA <26 252 2+3* 173 79 36+400* 31.3 98.9 74.3 -13 G A.O. <21 145 8+3* 72 73 137+400* 50.3 97.9 88.0 -50 E 21<26 145 2+3* 72 73+6^ 137+400* 52.3 99.1 88.9 -50 F *including FN/TN of Initial Assessment. ^including the observation group I.A.: Initial Assessment. MoCA: Montreal Cognitive Assessment. S.A.: stand-alone. A.O.: add-on. NPA: referred for a Neuropsychological assessment. FN: False negative. FP: False Positive. TP; True Positive.TN: True Negative. PPV: Positive Predictive Value. NPV: Negative Predictive Value. ACC: Accuracy. DIF: difference in referrals compared to I.A. 5.3.2 Single threshold The initial assessment resulted in 290 referrals for NPA (figure 1, column D). An accuracy of 69% was achieved for detecting MD (table 3), with 3 FNs. Using a single MoCA threshold of <21 to select those requiring an NPA resulted in a decrease in referrals but an increase in FNs compared to the initial assessment (Columns A and E). However, this resulted in an improvement in their accuracy (table 3). When the MoCA was used as an add-on to screen the ‘patients not suspected after initial assessment’ (n=403: table 4 d, calculations not shown), the accuracy deteriorated to 57% by adding 87 referrals to the initial set of 290 referrals, resulting in a total of 377 referrals (including 297 FPs). Comparing the PPVs and NPVs of the different selection strategies at a cut-off <21 for MD, we found a substantial increase in PPV and only a slight decrease in NPV when the MoCA was used as an add-on. When the cut-off was raised to <26 for detecting MD per strategy (columns C, G), the FNs decreased but with a substantial increase in referrals, which decreased the PPV and ACC.
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