Table 4.

Univariate meta regression results.

Variable		Coefficient (95% CI)	p-Value
Primary tumor site	Oral cavity	1 (reference)	-
	Oropharynx NOS	4.66 (−0.91; 10.22)	0.101
	Oropharynx HPV+	5.54 (0.16; 10.92)	0.044
	Mixed series	2.41 (−1.76; 6.58)	0.257
Geographic area	Europe	1 (reference)	-
	North America	0.25 (−3.00; 3.49)	0.881
	Asia	−3.47 (−6.73; −0.22)	0.037
	Other areas	−3.98 (−9.06; 1.10)	0.124
Publication year		−0.05 (−0.20; 0.09)	0.484

Abbreviations: CI = confident interval; HPV = human papilloma virus; NOS = not otherwise specified.