Table 1.

Receiver operating characteristic (ROC) analysis for the best-performing definition for loss to followup.

Cutoff (days)	Sensitivity (%)	Specificity (%)	Area under ROC	Cutoff (days)	Sensitivity (%)	Specificity (%)	Area under ROC
10	99.67	16.97	58.32	160	90.96	90.77	90.87
20	99.02	24.32	61.67	170	90.64	91.44	91.04
30	98.05	31.31	64.68	175	90.64	92.05	91.34
40	96.82	39.90	68.36	180	90.55	92.26	91.41
50	96.34	49.52	72.93	185	90.23	92.53	91.38
60	95.77	57.20	76.48	190	89.33	93.01	91.17
70	95.28	65.52	80.40	200	88.52	93.44	90.98
80	95.11	71.26	83.19	210	87.79	94.13	90.96
90	94.71	77.62	86.16	240	85.26	95.25	90.26
100	94.22	80.91	87.57	270	83.55	96.43	89.99
120	93.24	86.18	89.71	300	82.00	97.04	89.52
150	91.53	90.17	90.85	365	78.99	97.73	88.36

True LTFU defined as no patient followup in the 12 month prior to 31 March 2010. Each cutoff used as a potential definition of LTFU was the days between last clinical visit and 31 March 2009 in the March 2009 data transfer. The sensitivity and specificity of each cutoff in identifying true LTFU were calculated, and the optimal cutoff identified based on ROC analysis.