Table 3. Cut-off points and statistical parameters for three footprint analysis methods to identify factors associated with flatfoot, using clinical diagnosis as a gold standard.

40–64 years	Clarke’s angle	95% CI	Chippaux-Smirak index	95% CI	Staheli index	95% CI
Youden Index	0.758	(0.69–0.83)	0.462	(0.39–0.52)	0.372	(0.30–0.44)
Cut-off point	31.50		45.05		0.98
AUC	0.928	(0.899–0.957)	0.802	(0.763–0.842)	0.778	(0.746–0.810)
Sensitivity	83.76%	(75.54–89.70)	87.18%	(79.43–92.41)	54.07%	(47.62–60.38)
Specificity	92.05%	(89.96–93.75)	58.36%	(54.94–61.70)	83.19%	(80.23–85.88)
PPV	59.39%	(51.46–66.88)	22.52%	(18.81–26.70)	52.99%	(46.62–59.27)
NPV	97.61%	(96.22–98.51)	97.04%	(95.06–98.27)	83.83%	(80.85–86.44)
Prevalence	12.19%	(10.22–14.46)	12.19%	(10.22–14.46)	25.95%	(23.16–28.83)
PLR	10.54	(8.26–13.44)	2.09	(1.88–2.33)	3.23	(2.64–3.94)
NLR	0.18	(0.12–0.27)	0.22	(0.14–0.35)	0.55	(0.48–0.63)
≥65 years	Clarke’s angle	95% CI	Chippaux-Smirak index	95% CI	Staheli index	95% CI
Youden Index	0.713	(0.66–0.76)	0.420	(0.35–0.45)	0.373	(0.30–0.44)
Cut-off point	30.50		46.03		0.98
AUC	0.910	(0.888–0.931)	0.788	(0.757–0.819)	0.778	(0.746–0.810)
Sensitivity	86.59%	(81.53–90.46)	89.84%	(85.20–93.19)	54.07%	(47.62–60.38)
Specificity	84.76%	(81.83–87.29)	50.14%	(46.38–53.90)	83.19%	(80.23–85.88)
PPV	66.56%	(61.06–71.66)	38.70%	(34.72–42.85)	52.99%	(46.62–59.27)
NPV	94.75%	(92.62–96.30)	93.37%	(90.24–95.58)	83.83%	(80.85–86.44)
Prevalence	25.95%	(23.21–28.89)	25.95%	(23.21–28.89)	25.95%	(23.16–28.83)
PLR	5.68	(4.74–6.81)	1.80	(1.65–1.96)	3.23	(2.64–3.94)
NLR	0.16	(0.12–0.22)	0.20	(0.14–0.30)	0.55	(0.48–0.63)

AUC, area under the receiver operating characteristic curve; CI, confidence interval; NLR, negative likelihood ratio; NPV, negative predictive value; PLR, positive likelihood ratio; PPV, positive predictive value.