MDD - Bio: Genetics - Caspi et al. (2003)

What was the aim of the Caspi et al. (2003) study?

Determine whether there is evidence for the gene-environment interaction for a mutation of the neurotransmitter (serotonin transporter) reuptake gene (5-HTT)

What was the participant sample of the Caspi et al. (2003) study?

847 26yr old New Zealanders

How were groups split in the Caspi et al. (2003) study?

Based on their 5-HTT allele length: two short alleles (mutation), one short and one long allele, and 2 long alleles

What were the results of the Caspi et al. (2003) study?

People who had inherited one or more short versions of the allele demonstrated more symptoms of depression and suicidal ideation in response to stressful life events.

The effect was strongest for those with three or more stressful life events

What do the results of the Caspi et al. (2003) study suggest?

Simply inheriting a gene wasn’t enough to trigger it → It is the gene’s interaction w/ stressful life events that increases the likelihood of depression

What are the strengths of the Caspi et al. (2003) studyn in relation to causality?

The researchers exerted control by restricting the measurement of stressful life events in their sample as falling between the ages of 21 and 26 which should ensure a degree of consistency across the measurement thus increasing reliability

Conducting three separate correlational analyses means that each measure is checked by the findings of the other measures which should ensure internal validity.

What are the limitations of the Caspi et al. (2003) study in relation to bias?

• questionnaire relies on self-reported data: recall bias, social desireability bias, those w/ depression may be more likely to perceive and recall events as stressful → inflating correlation b/w stress and depression

• sample: New Zealanders, mostly european descent, 26yrs old

• biological reductionism: focusing on a single gene may oversimplify the etiology of depression

What are the limitations of the Caspi et al. (2003) study in relation to causality?

• Used a cross-sectional retrospective design: change is not observed over time → doesn’t support a causal inference

• Still correlational, as the gene itself isn’t manipulated

• limited external validity (Swedish, age, European ancestry)

What method was used to measure the three factors in Caspi et al (2003)?

Genetic variation: DNA testing

stressful life events: a self-report Life Stress Inventory (14 events b/w 21-26)

depression: standardised clinical interviews (DSM-IV criteria).

What are the strengths of the Caspi et al. (2003) studyn in relation to measurement?

• objective DNA analysis (reduces researcher bias + ensures consistent measurement)

• standardized interview for MDD diagnosis

What are the limitations of the Caspi et al. (2003) studyn in relation to measurement?

• stressful life events were assessed by self-report questionnaires: recall bias, social desireability bias, indiv, differences in emotional perception (coping style, mood, etc)

• indirect measurement of neurotransmitter reuptake protein