Twin Research

Articles

Defining discordance in twin studies of risk and protective factors for late life disorders

Margaret Gatza1 c1, Nancy L Pedersena2, Michael Crowea3 and Amy Fiskea4

a1 Department of Psychology, University of Southern California, Los Angeles, California, USA; Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Swedengatz@rcf.usc.edu

a2 Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden; Department of Psychology, University of Southern California, Los Angeles, California, USA

a3 Department of Psychology, University of Southern California, Los Angeles, California, USA

a4 Department of Psychology, University of Southern California, Los Angeles, California, USA

Abstract

In studies that employ matched pair analysis to identify environmental exposures important for a disorder, criteria for discordant pairs are seldom discussed. Yet several assumptions concerning the definition of discordancy may have considerable influence over what results are found. Problems are exacerbated when age of onset for a disorder is late in life. We propose a new set of criteria for defining discordant pairs in studies of dementia, taking into account duration of discordance and competing causes of mortality, and evaluate the consequences of choosing alternative definitions of discordancy. Twin Research (2000) 3, 159–164.

(Revised March 23 2000)

(Revised May 22 2000)

(Accepted June 06 2000)

Keywords

  • co-twin control;
  • Alzheimer's disease;
  • dementia;
  • genetic epidemiology

Correspondence:

c1 Correspondence: Dr Margaret Gatz, Department of Psychology, University of Southern California, 3620 McClintock, Los Angeles, California90089-1061, USA. Tel: 213 740 2212; Fax: 213 746 5994

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