Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Original Article
  • Published:

Stability of Wertheimer–Leeper wire codes as a measure of exposure to residential magnetic fields over a 9- to 11-year interval

Abstract

The Wertheimer–Leeper (W–L) wire code is a construct used as a surrogate indicator of residential exposure to electromagnetic fields. However, little is known about how changes in electrical distribution systems affect wire code assignment. The wire code was determined for 150 homes in the Seattle, WA, area twice, 9–11 years apart. For each home, the authors evaluated whether the electrical configuration around the home and the wire code changed between the two time points. The effect of wire code misclassification on observable odds ratios was evaluated, given hypothetical true control distributions and two different dose–response curves. There was an electrical configuration change for 77 (51.3%) homes, which resulted in a wire code change for 29 (19.3%) homes. Eight (5.3%) other homes had a wire code change due to mapping errors or methodological inconsistencies. Misclassification masked the shape of a threshold (nonlinear) dose–response curve and changed the slope of a linear dose–response curve. Although the wire code detected less than half of electrical configuration changes, misclassification of exposure over time may change odds ratios and mask possible dose–response relationships.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1

Similar content being viewed by others

References

  • Ahlbom, A, Day, N, Feychting, M, Roman, E, Skinner, J, Dockerty, J, Linet, M, McBride, M, Michaelis, J, Olsen, JH, Tynes, T, Verkasalo, PK . A pooled analysis of magnetic fields and childhood leukaemia, Br J Cancer (2000) 83: 692–698

    Article  CAS  Google Scholar 

  • Armstrong, BK, White, E, Saracci, R . Principles of exposure measurement in epidemiology, Monographs on Epidemiology and Biostatistics. Vol. 21 Oxford Univ. Press, Oxford, UK 1992 pp66–124

    Google Scholar 

  • Birkett, NJ . Effect of nondifferential misclassification on estimates of odds ratios with multiple levels of exposure, Am J Epidemiol (1992) 136: 356–362

    Article  CAS  Google Scholar 

  • Correa-Villasenor, A, Stewart, WF, Franco-Marina, F, Seacat, H . Bias from nondifferential misclassification in case–control studies with three exposure levels, Epidemiology (1995) 6: 276–281

    Article  CAS  Google Scholar 

  • Davis, S, Mirick, DK, Stevens, RG . Residential magnetic fields and the risk of breast cancer, Am J Epidemiol (2002) 155: 446–454

    Article  Google Scholar 

  • Dosemeci, M, Wacholder, M, Lubin, S . Does nondifferential misclassification of exposure always bias a true effect toward the null value? Am J Epidemiol (1990) 132: 746–748

    Article  CAS  Google Scholar 

  • Dovan, T, Kaune, WT, Savitz, DA . Repeatability of measurements of residential magnetic fields and wire codes, Bioelectromagnetics (1993) 14: 145–159

    Article  CAS  Google Scholar 

  • Greenland, S, Sheppard, AR, Kaune, WT, Poole, C, Kelsh, MA . A pooled analysis of magnetic fields, wire codes, and childhood leukemia. Childhood Leukemia-EMF Study Group, Epidemiology (2000) 11: 624–634

    Article  CAS  Google Scholar 

  • Hardell, L, Holmberg, B, Malker, H, Paulsson, LE . Exposure to extremely low frequency electromagnetic fields and the risk of malignant diseases—an evaluation of epidemiological and experimental findings, Eur J Cancer Prev (1995) 4: 3–107

    Article  Google Scholar 

  • Savitz, DA, Pearce, NE, Poole, C . Methodological issues in the epidemiology of electromagnetic fields and cancer, Epidemiol Rev (1989) 11: 59–78

    Article  CAS  Google Scholar 

  • Savitz, DA, Pearce, NE, Poole, C . Update on methodological issues in the epidemiology of electromagnetic fields and cancer, Epidemiol Rev (1993) 15: 558–566

    Article  CAS  Google Scholar 

  • Severson, RK, Stevens, RG, Kaune, WT, Thomas, DB, Heuser, L, Davis, S, Sever, L . Acute nonlymphocytic leukemia and residential exposure to power frequency magnetic fields, Am J Epidemiol (1988) 128: 10–20

    Article  CAS  Google Scholar 

  • Tarone, RE, Kaune, WT, Linet, MS, Hatch, EE, Kleinerman, RA, Robison, LL, Boice, JD Jr Wacholder, S . Residential wire codes: reproducibility and relation with measured magnetic fields, Occup Environ Med (1998) 55: 333–339

    Article  CAS  Google Scholar 

  • Wertheimer, N, Leeper, E . Electrical wiring configurations and childhood cancer, Am J Epidemiol (1979) 109: 273–284

    Article  CAS  Google Scholar 

  • Wertheimer, N, Leeper, E . Adult cancer related to electrical wire near the home, Int J Epidemiol (1982) 11: 345–355

    Article  CAS  Google Scholar 

  • Wrensch, M, Yost, M, Miike, R, Lee, G, Touchstone, J . Adult glioma in relation to residential power frequency electromagnetic field exposures in the San Francisco bay area, Epidemiology (1999) 10: 523–527

    Article  CAS  Google Scholar 

Download references

Acknowledgements

This research was supported by grant no. R01CA55844 from the National Cancer Institute. Shelley S. Tworoger was supported, in part, by the National Institutes of Environmental Health Sciences (NIEHS, NIH) Training grant T32EF07262. The authors thank the following individuals for their valuable contributions to this work: Norma Logan, project management; Elizabeth Carosso, data management; Neil Callahan, Yves Jaques and Cathy Kirkwood, data collection; and Peggy Adams Myers, contract administration. The authors also particularly thank Mark Reames, who was involved in data collection and helped with the visual map inspections.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to SHELLEY S TWOROGER.

Appendix

Appendix

Determining observable case–control exposure distributions and odds ratios from a hypothesized, true distribution and odds ratios, accounting for misclassification

Let,

  • VL=VLCC

  • OL=OLCC

  • OH=OHCC

  • VH=VHCC

(A) Choose parameter definitions:

  • OROL=odds ratio, OLCC versus VLCC

  • OROH=odds ratio, OHCC versus VLCC

  • ORVH=odds ratio, VHCC versus VLCC

  • n=number of controls

  • PVL=proportion of controls, VLCC

  • POL=proportion of controls, OLCC

  • POH=proportion of controls, OHCC

  • PVH=proportion of controls, VHCC

(B) Determine the true number of controls in each category:

  • NCo,VL=number of controls, VLCC=n*PVL

  • NCo,OL=number of controls, OLCC=n*POL

  • NCo,OH=number of controls, OHCC=n*POH

  • NCo,VH=number of controls, VHCC=n*PVH

(C) Determine the true number of cases in each category:

Let,

  • x=OROL(NCo,OL/NCo,VL)

  • y=OROH(NCo,OH/NCo,VL)

  • z=ORVH(NCo,VH/NCo,VL)

Then,

  • NCa,VL=number of cases, VLCC=n/(1+x+y+z)

  • NCa,OL=number of cases, OLCC=NCa,VL*x

  • NCa,OH=number of cases, OHCC=NCa,VL*y

  • NCa,VH=number of cases, VHCC=NCa,VL*z

(D) Determine the observable number of controls, using the misclassification matrix \(\overline{M}\) and the true case and control distributions, \(\overline{A}\) and \(\overline{B}\), respectively. Let:

where Ci,j is the proportion of those with true exposure category j (from the original study) classified as exposure category i in the validity study.

Then, the observable case and control distributions are \(\overline{C}\); and \(\overline{D}\), respectively, where:

Rights and permissions

Reprints and permissions

About this article

Cite this article

TWOROGER, S., DAVIS, S., SCHWARTZ, S. et al. Stability of Wertheimer–Leeper wire codes as a measure of exposure to residential magnetic fields over a 9- to 11-year interval. J Expo Sci Environ Epidemiol 12, 448–454 (2002). https://doi.org/10.1038/sj.jea.7500246

Download citation

  • Received:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/sj.jea.7500246

Keywords

Search

Quick links