When assessing twin concordance, use the probandwise not the pairwise rate

Area of Science:

• Psychiatry
• Genetics
• Twin Research

Background:

• Twin studies are crucial for understanding the genetic contributions to complex diseases like schizophrenia.
• Two primary methods for analyzing twin concordance rates exist: pairwise and probandwise.
• The probandwise rate is generally considered more appropriate for most applications in genetic research.

Purpose of the Study:

• To clarify the debate surrounding the use of pairwise versus probandwise concordance rates in schizophrenia twin studies.
• To address and correct the misinterpretation of twin study data by Torrey (1992) regarding genetic influence on schizophrenia.
• To reaffirm the validity of existing twin study findings on the significant genetic component of schizophrenia.

Main Methods:

• Review and comparison of the statistical methodologies of pairwise and probandwise concordance rates.
• Analysis of the implications of using pairwise rates versus probandwise rates in the context of schizophrenia twin studies.
• Critique of a specific review (Torrey, 1992) that utilized pairwise rates inappropriately.

Main Results:

• The probandwise concordance rate is statistically preferred over the pairwise rate for most twin study analyses.
• Torrey's (1992) conclusion of weaker monozygotic twin concordance for schizophrenia resulted from the incorrect application of pairwise rates.
• The continued analysis using appropriate methods strongly supports a substantial genetic contribution to schizophrenia.

Conclusions:

• The choice of concordance rate measure significantly impacts the interpretation of twin study findings.
• Schizophrenia twin research consistently demonstrates a robust genetic etiology.
• Correct application of statistical methods in twin studies is essential for accurate conclusions about genetic influences.