Open the app
  1. Home
  2. Lessons
  3. GCSE Psychology
  4. Key study: Caspi et al. (2003) life stress and the 5-HTT gene

Key study: Caspi et al. (2003) life stress and the 5-HTT gene

🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.

Why do some people become depressed after hard times while others do not? Caspi and colleagues looked at genes and life stress together.

Aim and procedure

Aim: to investigate why stressful life experiences lead to depression in some people but not others, by testing whether the 5-HTT gene moderates the effect of stress.
Sample: from the Dunedin study in New Zealand, which followed 1,037 children born in the early 1970s. The analysis used 847 white (non-Maori) participants, put into three groups:
two short alleles (s/s): 147 people (17%)
one short and one long (s/l): 435 people (51%)
two long alleles (l/l): 265 people (31%)
Procedure: a longitudinal study: participants were assessed many times from age 3 and again at age 26. Stressful life events between ages 21 and 26 (14 events, including employment, financial, housing, health and relationship stress) were recorded with a life-history calendar. Depression at 26 was assessed using a diagnostic interview, plus questionnaires from informants who knew the person well.

Results and conclusion

Results: the three gene groups did not differ in how many stressful events they had.
People with one or two short alleles showed more depressive symptoms, more diagnosed depression and more suicidal thoughts after stressful life events than people with two long alleles.
Childhood maltreatment predicted adult depression only in people with a short allele.
Conclusion: there is a gene-environment interaction: the short allele makes people more vulnerable to depression, but mostly when they experience stress. This supports the diathesis-stress idea.

Strengths and weaknesses

Strengths: a large sample studied longitudinally, so life events were recorded as they happened. It used more than one measure of depression (interview and informants), increasing validity. It considers both nature and nurture.
Weaknesses: stressful life events were self-reported, so may be inaccurate. The sample was all from one place and all white New Zealanders, so it may not generalise. Later studies trying to repeat the gene-stress finding have had mixed results.
Worked example

Two people both lose their jobs and go through a break-up. One has two short 5-HTT alleles, the other two long alleles. What would Caspi et al. predict?

  1. Both have high stress.
  2. The short allele increases vulnerability to depression when stress happens.

Answer: The person with two short alleles is more likely to become depressed.

Key idea

Caspi et al. studied 847 New Zealanders from the Dunedin study. People with one or two short 5-HTT alleles were more likely to become depressed after stressful life events than those with two long alleles. This shows a gene-environment interaction. Large and longitudinal, but life events were self-reported.

Check you have got it

Answer 7 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.

Practise this lesson free (7 questions)All GCSE Psychology lessons