Kendler et al (2006)

Question 1

Correlational Study

Answer 1

looks at the relationship between two or more variables, non-experimental,
does not manipulate or control any variables

Question 2

Inheritance

Answer 2

: The transmission of physical or psychological traits from parents to their offspring

Question 3

Aim

Answer 3

Determine the role that genetics plays in MDD. Investigate three questions: Heritability of
MDD in Swedish sample, differences in heritability, and if genetic and environmental factors in
MDD differ over time

Question 4

Procedure

Answer 4

• Sample of twins listed in national Swedish registry
• Carried out telephone interviews that assessed lifetime MDD by using modified DSM-IV
  criteria
• Roughly 8000 twins met the criteria for a diagnosis of MDD at some point in their life
• Interviews asked about “shared environment” (when they lived together) and “individualspecific environment” (living situation in adult life)

Question 5

Results

Answer 5

• Heritability of MDD was significantly higher in women than men
• Correlations were significantly higher in MZ twins than in DZ twins
• Suggests that some genetic risk factors for MDD are sex-specific

Question 6

Evaluation

Answer 6

Correlational- no cause-and-effect relationship- no particular genes were isolated
- Confirm previous research- reliability
- Information about stressful life events was self-reported (men may be less reliable in
reporting their lifetime major depression)
- Interviewers did not officially diagnose twins and they accepted diagnoses made by
clinicians (not highly reliable) and by making diagnoses through telephone may lack
validity
- Large sample size