Table 2. Pooled risk estimates of HT for PTC risk (HT versus non-HT) according to the strata of selected covariates.

	No. of studies	OR (95% CI)	P for heterogeneity
Overall	27	2.12 (1.78-2.52)
Study design
Cohort	5	2.46 (1.07-5.66)	0.0003
Case-control	22	2.03 (1.72-2.41)	< 0.00001
Study method
Thyroidectomy	18	2.34 (1.97-2.76)	< 0.00001
FNA	6	1.27 (0.77-2.11)	< 0.0001
Selective FNA	3	2.37 (0.51-11.11)	0.002
Geographic area
Europe	11	1.56 (1.01-2.40)	< 0.00001
Asia	9	2.79 (2.15-3.61)	< 0.00001
America	7	1.92 (1.56-2.35)	0.07
Publication year
≥ 2010	20	2.32 (1.94-2.78)	< 0.00001
< 2010	7	1.65 (1.06-2.55)	< 0.00001
No. of PTCs
≥ 100	18	2.12 (1.75-2.56)	< 0.00001
< 100	9	1.98 (1.16-3.37)	0.003
Tumor subtype
PTC	24	2.06 (1.73-2.47)	< 0.00001
TC	3	2.64 (0.66-10.50)	0.002
Quality score
≥ 7	2	4.79 (0.49-46.92)	0.11
< 7	22	2.06 (1.73-2.44)	< 0.00001
Adjusted for multivariate
Yes	6	2.33 (1.32-4.14)	< 0.00001
No	21	1.88 (1.51-2.34)	< 0.00001
Mean age (year)
≥ 48	15	1.98 (1.54-2.53)	< 0.00001
< 48	7	1.94 (1.41-2.67)	0.004
Sex ratio (female:male)
≥ 5	10	2.17 (1.41-3.35)	< 0.00001
< 5	12	1.99 (1.61-2.45)	< 0.00001
Mean nodule size (cm)
≥ 1.3	5	2.09 (1.64-2.66)	0.005
< 1.3	4	3.38 (2.56-4.46)	0.16

No., number; OR, odds ratio; CI, confidence interval; FNA, fine-needle aspiration; PTC, papillary thyroid carcinoma; TC, thyroid cancer.