Diathesis–stress model
IB Psychology· Biological approach· 11 min read
1. Core concept
The diathesis–stress model says a behaviour or disorder appears when a predisposition (the diathesis — often genetic) meets a trigger (stress from the environment). Neither alone is enough: a vulnerable person can stay well without stressors, and a resilient person can weather the same stress. It explains why the same event affects people so differently, and why genes and environment must be studied together rather than separately.
2. Key studies
IB Psychology answers must be supported by named studies. Learn these to cite as evidence:
Caspi et al. (2003)
People with the short 5-HTT allele showed more depressive symptoms after stressful life events than long-allele carriers, while the genotype alone did not predict depression. — The textbook demonstration of gene × environment — the vulnerability expressed only when the stressor was present.
3. Evaluation (AO3)
Strength — interactionist fit — Explains the data better than gene-only or environment-only accounts and predicts individual differences in response to the same event.
Limitation — measurement & replication — 'Diathesis' and 'stress' are hard to operationalise, and some large replications of Caspi were weaker, so the effect size is debated.
4. Scope
5. Common Pitfalls
Wrong move:
A genetic predisposition makes the outcome fixed or inevitable.
Why:
A frequently penalised misconception in IB Psychology exams.
Correct move:
The diathesis only raises risk; without the environmental trigger it may never express — that is the entire point of the model.
Going deeper
- Genetic inheritancethe genetic predisposition side is genetic inheritance (BIO_6).
- Biological reductionismthis model is the interactionist reply to biological reductionism (BIO_2).