Article |

Schizophrenia in the NAS-NRC Panel of 15,909 Veteran Twin Pairs

Axel Hoffer, MD; William Pollin, MD
Arch Gen Psychiatry. 1970;23(5):469-477. doi:10.1001/archpsyc.1970.01750050085012.
Text Size: A A A
Published online

THE CLASSICAL twin method has played a major role in influencing the direction of psychiatric thought on the relative importance of heredity and environment in the pathogenesis of schizophrenia. Fundamentally, this method is a comparison of a group of monozygotic or "identical" twins with a group of dizygotic or "fraternal" twins. The percentage of pairs where both twins are affected by a particular disease is compared in the two groups. This percentage is called the pairwise concordance rate. Since monozygotic twins are assumed to be genetically identical, while dizygotic twins no more so than nontwin siblings, comparisons of concordance rates between these two groups have been used to estimate the genetic contribution to a given illness.

In the past, studies showing a high concordance rate for schizophrenia in monozygotic twins and a much lower one in dizygotic twins have been accepted as


Sign In to Access Full Content

Don't have Access?

Register and get free email Table of Contents alerts, saved searches, PowerPoint downloads, CME quizzes, and more

Subscribe for full-text access to content from 1998 forward and a host of useful features

Activate your current subscription (AMA members and current subscribers)

Purchase Online Access to this article for 24 hours

First Page Preview

View Large
First page PDF preview





Meets CME requirements for:
Browse CME for all U.S. States
Accreditation Information
The American Medical Association is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The AMA designates this journal-based CME activity for a maximum of 1 AMA PRA Category 1 CreditTM per course. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Physicians who complete the CME course and score at least 80% correct on the quiz are eligible for AMA PRA Category 1 CreditTM.
Note: You must get at least of the answers correct to pass this quiz.
You have not filled in all the answers to complete this quiz
The following questions were not answered:
Sorry, you have unsuccessfully completed this CME quiz with a score of
The following questions were not answered correctly:
Commitment to Change (optional):
Indicate what change(s) you will implement in your practice, if any, based on this CME course.
Your quiz results:
The filled radio buttons indicate your responses. The preferred responses are highlighted
For CME Course: A Proposed Model for Initial Assessment and Management of Acute Heart Failure Syndromes
Indicate what changes(s) you will implement in your practice, if any, based on this CME course.
Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).
Submit a Comment


Some tools below are only available to our subscribers or users with an online account.

Sign In to Access Full Content

Related Content

Customize your page view by dragging & repositioning the boxes below.