Caspi et al

Design Type

quasi-experiment

Topic

Research methods used in bio; genetic inheritance on behaviour

Aim

To investigate the role of gene mutation and epigenetics in MDD

Sample

847 New Zealand 26-year-olds

Procedure

1. All members of a cohort that had been assessed for mental health on an every-other-year basis until age 26.

2. Divided into three groups (group 1-> two short alleles; group 2 -> one short and one long allele; group 3 -> 2 long alleles).

3. The mutation of the 5-HTT has the short alleles.

4. Ps were asked to fill out a "stressful life events" questionnaire.

5. Asked about the frequency of 14 different events--including financial, employment, and relationship stressors--between the ages of 21 and 26.

6. Assessed for depression, aswell.

Findings

- People who inherited 1+ short alleles demonstrate more symptoms of depression and suicidal ideation in response to stress.

-The effect was strongest for those with 3+ stressful life events.

-Gene itself did not lead to depression, but increased the likelihood.

Strengths

Holistic approach

Large sample

Limitations

correlational, self-reported, self-fulfilling prophecy, low rel.