Table 2. Baseline imbalance in studies included in the meta-analysis.

	Primary tumor			Liver metastases
Study	Location	T Stage	N Stage	Number	Maximum diameter	Bilobar distribution	Major hepatectomy	Preoperative chemotherapy
Total number of studies with baseline imbalance	3	1	0	12	9	5	11	6
Abbott 2012	Na	N	N	Y	NA	NA	Y	N
Alexandrescu 2012	Nb	NA	NA	Nc	Nf	NA	N	Y
Brouquet 2010	Nb	NA	N	Ne	Yg	Y	Y	NA
Capussotti 2007	Nb	NA	N	Nc	Nf	N	Y	NA
Chua 2004	Na	NA	NA	Nc	Ng	N	Y	NA
de Haas 2010	Na	N	N	Yc	Ng	N	NA	Y
Hu 2013	Nb	NA	N	Nc	NA	N	N	NA
Luo 2010	Nb	Y	N	Yc	NA	NA	Y	Y
Martin 2003	Ya	NA	NA	Yc	Yf	NA	Y	NA
Martin 2009	Na	NA	N	Ne	Yg	NA	N	Y
Mayo 2013	Nb	NA	NA	Nc	Yg	N	Y	N
Moug 2010	Na	N	N	N	NA	NA	N	N
Reddy 2007	Nb	N	N	Yc	Yg	NA	Y	Y
Slupski 2009	Na	N	N	Ye	Yg	NA	N	N
Tanaka 2004	Nb	N	N	Ye	Yg	Y	Y	N
Thelen 2007	Ya	N	N	Yd	Nf	N	Y	Y
Turrini 2007	Nb	N	N	Yd	NA	Y	NA	NA
Vassiliou 2007	Ya	NA	NA	Yd	N	N	N	NA
Wang 2008	Nb	N	N	Nd	Nf	Y	NA	NA
Weber 2003	Na	N	N	Yd	Nf	N	Y	NA
Xu 2009	Na	N	N	Nd	Yf	N	N	NA
Yan 2007	Na	NA	N	Yd	Yg	Y	N	NA

Y: significant imbalance of baseline; N: no significant imbalance of baseline; NA: data not available.

Location was compared as: (right-sided vs. left-sided vs. rectum)^a or (colon vs. rectum)^b. When compared as (right-sided vs. left-sided vs. rectum)^a, the transverse colon was included in the right-sided, the sigmoid colon was included in the left-sided.

T stage was compared as T1+T2 vs. T3+T4.

N stage was compared as N0 vs. N+.

Number of metastases was compared as: (single vs. multiple)^c or (≤3 vs. >3)^d or (mean ± SD)^e or others with no superscript.

Maximum diameter of metastases was compared as: (≤5 cm vs. >5 cm)^f or (mean ± SD)^g or others with no superscript.

Major hepatectomy was defined as resection with ≥3 segments.

Preoperative chemotherapy included chemotherapy before both primary resection and hepatectomy.

The study Vassiliou 2007 enrolled only patients with ≤3 liver metastases.