Table 2. The results of subgroup-analyses of the relationship between plasma prolaction levels and breast cancer risk according to various factors.

Group	No. Of study	RR (95% CI)	P for heterogeneity	I2
All	7	1.16 [1.04,1.29]	0.372	7.4%
Menopause status
Premenopause	7	0.99 [0.84,1.16]	0.447	0.0%
Postmenopause	7	1.27 [1.13,1.43]	0.282	19.4%
ER/PR status
ER+/PR+	3	1.26 [1.04,1.53]	0.007	80.1%
ER+/PR−	1	1.61 [0.98,2.65]	NA	NA
ER−/PR−	3	1.00 [0.70,1.43]	0.795	0.0%
Morphology
In situ	2	1.29 [1.04,1.61]	0.540	0.0%
Invasive	2	1.32 [1.07,1.63]	0.276	15.9%
Study design
Cohort	6	1.36 [1.18,1.56]	0.832	0.0%
Case-control	1	0.47 [0.20,1.10]	NA	NA