Which of the following scenarios would most effectively demonstrate a violation of the "equal environments assumption" in twin studies?

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Question restatement: The prompt asks which scenario would most effectively demonstrate a violation of the equal environments assumption (EEA) in twin studies.

Option A: 'Monozygotic twins are treated more similarly by their parents compared to dizygotic twins.' This directly describes a situation where MZ and DZ twins experience different environments due to parental treatment. If MZ twins share more similar environments than DZ twins, and yet their traits appear more similar, the increased concordance could be due to environmental similarity rather than purely genetic similarity, thereby illustrating an EEA violation. This is the classic, textbook example of a violation.

Option B: 'Monozygotic twins show higher concordance rates for a trait than dizygotic twins raised in the same environment.' While this suggests a genetic influence (MZ similarity > DZ similarity), it does not specify a difference in environmental treatment or environments between the twin types. If both are raised in the same environment, this scenario aligns with the standard heritability inference rather than demonstrating an EEA violation. So it doesn’t demonstrate a violation per se.

Option C: 'Monozygotic twins experience greater environmental variability than dizygotic twins.' This would imply MZ twins have more diverse environments, which could in theory affect outcomes, but it is not the canonical way EEA violations are demonstrated. The EEA concerns environmental similarity between twin types, not which type experiences more variability overall.

Option D: 'Dizygotic twins are raised in households with greater socioeconomic disparities than monozygotic twins.' This describes a between-family environmental difference that could influence comparisons, but it is less directly about the relative environmental similarity between MZ and DZ twins within the study design, making it a less clear demonstration of EEA violation.

Option E: 'None of the above.' Given that A clearly describes a scenario of differential treatment between MZ and DZ twins, this option would not be correct because there is a scenario that demonstrates the violation.

In summary, the essence of an EEA violation is that the environments of MZ and DZ twins are not equally similar. Option A captures that mismatch in environmental similarity most explicitly, whereas the other options either describe genetic effects under equal environments or describe environmental differences that do not directly illustrate the core violation in how the EEA is tested. The reasoning emphasizes how one would interpret twin concordance in light of environmental similarity, and why the other options fail to demonstrate the violation as clearly.

PSYC_V 305 991 2025W1 Unit 1 Exam

Which of the following scenarios would most effectively demonstrate a violation of the "equal environments assumption" in twin studies?

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