Table 2. Summary of 23 case-control studies on exposure to electric and magnetic fields and breast cancer in females.

No	1st author, year of publication and country	Cases	Controls	Exposure assessment method	The matched factors between cases and controls	Study period	OR (95%CI)	Scores
1	Vena JE(1991), USA	378 postmenopausal women in the Western New York Study of Breast Cancer	438 controls randomly selected from community	Frequency and mode of use of electric blankets	Age, region	1987–1989	0.89(0.67,1.19)
2	Loomis DP(1994), [15] USA	27882 Cases were female residents for 20 years and older at their death in 24 states.	110949 controls were random sample of women who died of any other underlying cause, excluding leukemia and brain cancer.	Job title.	Year of death, age, region	1985–1989	1.36(1.03,1.79)	6
3	Vena JE(1994), USA	290 premenopausal women who were admitted to hospitals in Niagara and Erie counties	289 controls who were residents of the same two counties, randomly selected from the New York State driver's license records	Histories of electric blanket use	Age, region	1986–1991	1.14(0.81,1.59)	5
4	Coogan PF(1996), USA	6888 cases were female residents of four states with incident breast cancer reported to four tumor registries	9529 controls were randomly selected from state driver's license lists and health care telephone number	Job title	Age, region	1988–1991	1.00(0.90,1.11)	7
5	Li C-Y(1997), Taiwan	1980 cases were residents of northern Taiwan reported to the National Cancer Registry of Taiwan	1880 controls were random selection of women with cancers excluded these cancers associated with magnetic field exposure	Measurement and Estimation of magnetic fields in the residencies	Age, sex, and date of diagnosis	1990–1992	1.10(0.93,1.31)	5
6	Coogan FP(1998) [12], USA	259 cases were permanent residents of five towns and reported to the Massachusetts Cancer Registry.	738 controls resided in the towns were selected by random digit dialing, lists of Medicare beneficiaries, and death certificates.	Use of electric bed-warming devices and electric heat, Occupational history and residential history	Age, region	1983–1986	0.99(0.74,1.33)	7
7	Gammon (1998), USA	1645 incident cases were residents of one of three US geographic areas with a tumor registry.	1498 controls were identified via random digit dialing	Use of electric blankets	Age, region	1990–1992	1.06(0.92,1.22)	6
8	Feychting M(1998) [13], Sweden	669 cases were identified through record linkage to the Swedish Cancer Registry.	669 controls were selected randomly among those who were included in the study base.	The magnetic field at home were assessed through theoretical calculations	Age, lived in the same parish, and lived near the same power line.	1960–1985	1.14(0.86,1.51)	6
9	Zheng (2000), USA	608 Cases either had breast-related surgery at the Yale-New Haven Hospital, or who were residents of Tolland County	609 controls had had breast-related surgery and who were histologically diagnosed with normal tissue or benign breast diseases.	Use of electric blankets	Age, region	1994–1997	0.86(0.69,1.09)	5
10	McElroy JA (2001) [21], USA	1,949 cases were identified from state wide tumor registries in Massachusetts, New Hampshire, and Wisconsin	2,498 cases were randomly selected from population lists as controls.	Electric blanket and mattress cover use	Age	June 1994–July 1995	0.97(0.86,1.09)	6
11	Wijngaarden (2001), USA	843 cases were identified through the North Carolina Central Cancer Registry	773 Controls were sampled from lists of the Division of Motor Vehicles and Health Care Financing Administration	Cumulative exposures to magnetic fields were based on a measurement survey.	Age, race	1993–1995	0.94(0.76,1.16)	7
12	Davis S(2002),USA[23]	813 cases were identified by the Cancer Surveillance System of the Fred Hutchinson Cancer Research Center.	793 controls were resident and identified by random digit dialing.	Measurements in the home and self-reported measures of at-home electric appliance use.	Race, age and region	November 1992–March 1995	0.99(0.77,1.28)	7
13	Kabat GC (2003a) [22],USA	1323 cases were identified from Health Care Financing Administration files was from the Long Island Breast Cancer Study Project (LIBCSP)	1362 controls were from the LIBCSP and controls were residents identified by random digit dialing and Health Care Financing Administration (HCFA) rosters.	Electric blanket use	Age, region	August 1, 1996 to July 31, 1997.	1.11(0.94,1.30)	6
14	Kabat GC(2003b) [22],USA	666 cases was from the Electromagnetic Fields and Breast Cancer on Long Island Study (EBCLIS*)	I 557 controls were from EBCLIS	Electric blanket use	Age, region, long-term residents	August 1, 1996 to July 31, 1997.	0.97(0.76,1.23)	5
15	Schoenfeld ER (2003) [16], USA	576 cases was from the EBCLIS	585 controls were from EBCLIS	In-home EMF measurements, wire mapping of overhead power lines	Age, region, long-term residents	August 1, 1996, to June 20, 1997.	1.03(0.82,1.30)	7
16	Kliukiene J (2003) [17],Norway	99 breast cancer cases from a cohort of Norwegian female radio and telegraph operators.	396 controls from the cohort alive at time of diagnosis.	Calculated based on employment information. Magnetic field measurements	Age, region	January 1961 to the end of May 2002.	1.46(0.78,2.70)	6
17	Labreche F(2003)[19], Canada	608 cases were identified from records of pathology departments and cancer registries from hospitals.	667 controls had 32 different types of cancer from the same hospitals.	Job	Age, same hospital	1996–1997	1.22(0.93,1.61)	5
18	London SJ (2003) [24], USA	347 cases were identified by linkage to county and state tumor registries in Los Angeles County, California.	286 Controls were selected from a random sample of cohort members without breast cancer at baseline.	Exposure was assessed by means of wiring configuration coding	Race, age and region	1993–1999	1.26(0.87,1.83)	8
19	Zhu K, 2003(2003) [3], USA	304 cases lived in one of three Tennessee counties were identified through the Tennessee Cancer Reporting System.	305 controls were selected through random digit dialing.	Electric blanket use	Race, age and county	1995–1998	1.49(0.99,2.23)	6
20	Kliukiene J (2004) [17],Norway.	1830 cases of breast cancer were identified in a cohort of women living near a high-voltage power line in Norway.	The 3658 controls were selected randomly from the cohort.	Residential exposure by the lines, occupational exposure by job title, Magnetic field measurements for estimated time weighted average;	Age, region	1986–1996	1.53(1.28,2.85)	9
21	Forssen (2000) UM[25], Sweden	440 cases living within 300 meters of transmission lines in the cohort were identified from the Swedish Cancer Registry.	439,One matched control per case at random was selected.	Residential exposure by the power lines, and occupational exposure by job title,	Age, region, type of house, power line	1960–1985	1.02(0.78,1.35)	8
22	Forssen UM(2005), Sweden	18365 cases were identified from the cancer registry gainfully	101973 controls were selected randomly from the study base.	Job-exposure matrix based on personal magnetic field measurements	Rgion	1976–1999	1.04(0.99,1.08)	6
23	McElroy JA (2007) [20],USA	6213 cases were identified through the North Carolina Central Cancer Registry.	7390 Controls were sampled from lists of the Division of Motor Vehicles and rosters of Medicare beneficiaries.	Job title	Age, region	1970–2002	1.06(0.99,1.14)	6

*:Women eligible for EBCLIS were those LIBCSP participants who had lived in their current residences for 15 years or more (long-term residents).