Table 1. Validity of the GP rating of driving activity

		Patient report (reference):'Do you drive a car?'		Total	Predictive values (95% CI)
		Yes	No	Total	Predictive values (95% CI)
GP rating: 'Does the patient currently drive a car?'	Yes	49	18 ^a	n = 67	PPV 73.1(63.1 to 81.3)
GP rating: 'Does the patient currently drive a car?'	No	24 ^b	336	n = 360	NPV 93.3(91.5 to 94.9)
Total		n = 73	n = 354	n = 427
Test accuracy (95% CI):		Sensitivity 67.1 (57.9 to 74.6)	Specificity 94.9 (93.0 to 96.5)		Concordance:Cohen’s ƙ = 0.64 (95% CI 0.53 to 0.74)

^aIncluding 15 x GP rating 'don't know'. ^bIncluding 8 x GP rating 'don't know'. CI = confidence interval. PPV = positive predictive value. NPV = negative predictive value.