title: Defining discordance in twin studies of risk and protective factors for late life disorders.
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.
authors.affiliation: Department of Psychology, University of Southern California, Los Angeles, California 90089-1061, USA. gatz@rcf.usc.edu
authors.forename: M
authors.initials: M
authors.lastname: Gatz
authors.forename: N L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: M
authors.initials: M
authors.lastname: Crowe
authors.forename: A
authors.initials: A
authors.lastname: Fiske
mesh_terms: D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000453:epidemiology / Q000235:genetics; D016022:Case-Control Studies; D003704:Dementia / Q000453:epidemiology / Q000235:genetics*; D004200:Diseases in Twins; D004781:Environmental Exposure; D006801:Humans; D017720:Molecular Epidemiology; D016017:Odds Ratio; D018570:Risk Assessment; D012307:Risk Factors; D018433:Twin Studies as Topic; D014427:Twins