Caspi et al. (2003): stress, genes & depression

The detail the scheme rewards here. Not creditworthy: "people with the short gene get depressed" — his carriers with no such events were barely different. Creditworthy: "a short allele raised the risk only when the person had also had several stressful life events." If your sentence holds with no stressful events, you have dropped the interaction — and the mark.

Candidates write up a different study's participants entirely. Learn this sample as four hooks: 847 people, a birth cohort in Dunedin, New Zealand, followed since childhood, all assessed at age 26, sorted by genotype into 147 s/s, 435 s/l and 265 l/l. If your answer says "university students" or "clinic patients", it is not this study.

"More depressed" and "more depressive symptoms" is one point twice, scoring once. Pair findings from different rows: (1) as stressful events rose, short-allele carriers showed more depression; (2) those with two long alleles showed almost no rise. The flat l/l line is what makes the study an interaction, so it is the stronger second point.

A result is what was observed ("short-allele carriers grew more depressed as their events rose"). A conclusion is what the researcher infers from it ("the short allele is a vulnerability that shows only under stress — a gene-environment interaction"). Recycling the numbers is not a conclusion: name what the pattern means, not what it was.

"A weakness is that it was only done in New Zealand" identifies but does not justify — it earns the identification mark at most. Add the consequence: "so the pattern may not hold where the balance of short and long alleles differs, which limits generalisability." Use point, why, consequence every time.

Nature = behaviour from inherited, biological factors (the genotype here). Nurture = behaviour from environment and experience (the stressful life events). Candidates swap them between parts, or answer on nature when nurture was asked. Tie each label to the right side of the study — and Caspi shows the two acting together, so it is neither alone.

"Caspi found a gene for depression, so this is nature" — all wrong. No gene was found: the short allele mattered only alongside life stress. Not nature-only: it is an interaction, nature and nurture each shaping the other. No proof of cause: genotype occurred naturally, so it shows a pattern, not a cause; explaining it by one gene alone is reductionist.