Table 3. Optimal waist-height cut-off values and measures of performance in the derivation sample.

WHtR thresholds	Methods	Sensitivity	Specificity	PPV	NPV	Youden index
Overall
0.465	Youden index	0.419	0.772	0.142	0.937	0.191
0.435	CTL	0.562	0.595	0.111	0.938	0.157
0.500		0.305	0.858	0.162	0.932	0.163
Boys
0.455	Youden index	0.429	0.884	0.351	0.914	0.313
0.425	CTL	0.603	0.677	0.213	0.921	0.280
0.500		0.254	0.940	0.381	0.896	0.194
Girls
0.465	Youden index	0.500	0.695	0.086	0.96	0.195
0.465	CTL	0.500	0.695	0.086	0.96	0.195
0.500		0.381	0.809	0.103	0.958	0.190
Rural
0.415	Youden index	0.818	0.396	0.129	0.952	0.214
0.415	CTL	0.818	0.396	0.129	0.952	0.214
0.500		0.182	0.851	0.118	0.905	0.033
Semi-rural
0.505	Youden index	0.316	0.871	0.222	0.916	0.187
0.455	CTL	0.447	0.711	0.153	0.917	0.158
0.500		0.316	0.849	0.197	0.914	0.165
Urban
0.475	Youden index	0.451	0.808	0.146	0.952	0.259
0.435	CTL	0.647	0.593	0.105	0.958	0.240
0.500		0.333	0.862	0.152	0.946	0.195
Black
0.465	Youden index	0.500	0.754	0.120	0.957	0.254
0455	CTL	0.536	0.699	0.107	0.957	0.235
0.500		0.357	0.832	0.125	0.951	0.189
Coloured
0.425	Youden index	0.644	0.563	0.121	0.944	0.207
0.425	CTL	0.644	0.563	0.121	0.944	0.207
0.500		0.288	0.877	0.179	0.930	0.165
White
0.475	Youden index	0.444	0.759	0.229	0.895	0.203
0.445	CTL	0.556	0.634	0.196	0.899	0.190
0.500		0.278	0.839	0.217	0.878	0.117

CTL, closest top left; NPV, negative predictive value; PPV, positive predictive value; WHtR, waist-to-height ratio.