With the exception of occupational exposure, no other surrogate for deciding who was or was not exposed to EMFs has been discovered. The codes first appeared in N. Wertheimer and E. Leeper: Am. J. Epidemiol. 109:273, 1979. The validity of the individual WL codes was never established, but when grouped (end pole + OLCC = Control; OHCC + VHCC = EMF) they were shown to code for EMF exposure in all 4 studies in which the issue was considered.

REFERENCE	LOCATION		MAGNETIC FIELD (mG)
			EMF RESIDENCES	CONTROL RESIDENCES
1	Denver, CO	Median	1.6 (N=190)	0.5 (N=227)
2	Denver, CO	Mean	1.3 (N=100)	0.6 (N=334)
		Median	1.0 (N=100)	0.4 (N=334)
3	Seattle, WA	Mean	1.4 (N=13)	0.5 (N=26)
4	Los Angeles, CA	Mean	0.9 (N=326)	0.6 (N=345)
		Median	0.8 (N=326)	0.5 (N=345)

1. N. Wertheimer and E. Leeper: Int. J. Epidemiol. 11:345, 1982.

2. D.A. Savitz, H. Wachtel, F.A. Barnes, E.H. John, J.G. Tvdik: Am. J. Epidemiol. 128:21, 1988.

3. W.T. Kaune, R.G. Stevens, N.J. Kallahan, R.K. Severson and D.B. Thomas: Bioelectromagnetics 8:315, 1987.

4. S.J. London, D.C. Thomas, J.D. Bowman, E. Sobel, T.C. Cheng and J.N. Peters: Am. J. Epidemiol. 134:923, 1991.

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