Table 2 Ablation analysis of the proposed approach by testing set.

Methods	Ultrasound characteristics							Evaluation indices (point estimation (95% CI))
Methods	Target sign	Equal sign	Funnel sign	Pseudo-target sign	Line sign	Colorectal dilatation	Enterolithiasis	Youden index	DOR	AUC of the ROCC	AUC of the PRC
Proposed approach ^$	√	√	√	√	√	√	√	0.86 (0.79–0.93)	401.63 (142.21-1144.50)	0.931 (0.902–0.953)	0.86 (0.77–0.92)
Su³ and Ochoa ^{17 #}	√	√				√	√	0.74 (0.65–0.83)	99.66 (45.16-219.18)	0.869 (0.833-0.900) ^a	0.74 (0.64–0.82) ^d
Lee ^{16 #}	√					√	√	0.65 (0.55–0.76)	49.84 (24.83-100.26)	0.827 (0.788–0.862) ^b	0.66 (0.55–0.75) ^e
Indirect signs ^#						√	√	0.43 (0.51–0.57)	13.99 (7.62–25.78)	0.714 (0.669–0.757) ^c	0.47 (0.37–0.58) ^f

DOR, diagnositc odds ratio; AUC, area under curves; ROCC, receiver operating characteristic curve; PRC, precision-recall curve; CI, confidence interval.
^$ A case would be considered as anal atresia if any of the “target sign,” “equal sign,” “funnel sign,” “pseudo-target sign,” or “line sign” existed. Colorectal dilatation and enterolithiasis are minor features suggesting fetal anal atresia only in coexistence with the aforementioned signs.
^# A case would be considered as anal atresia if any of the ticked features existed.
^a the difference in AUC (ΔAUC) compared to the proposed approach is 0.06, the 95% CI ranges from 0.03 to 0.10, and the P value is below 0.001 according to the DeLong method;.
^b the ΔAUC compared to the proposed approach is 0.10, the 95% CI ranges from 0.03 to 0.15, and the P value is below 0.001 according to the DeLong method;.
^c the ΔAUC compared to the proposed approach is 0.22, the 95% CI ranges from 0.15 to 0.28, and the P value is below 0.001 according to the DeLong method;.
^d the ΔAUC compared to the proposed approach is 0.12, and the 95% CI ranges from 0.07 to 0.19 according to the Bootstrap method;.
^e the ΔAUC compared to the proposed approach is 0.20, and the 95% CI ranges from 0.13 to 0.28 according to the Bootstrap method;.
^f the ΔAUC compared to the proposed approach is 0.39, and the 95% CI ranges from 0.30 to 0.47 according to the Bootstrap method.

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