What causes unipolar depression?
Explaining unipolar depression: its characteristics, the influence of genes (Caspi et al. 2003), and the cognitive theory of depression (Beck's negative triad and faulty thinking).
A focused answer to Edexcel GCSE Psychology Topic 3, covering unipolar depression: its characteristics, the influence of genes (Caspi et al. 2003) and the cognitive theory of depression (Beck's negative triad).
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What this dot point is asking
Edexcel wants you to describe unipolar depression and two explanations of it: the influence of genes (using Caspi et al. 2003) and the cognitive theory (Beck's negative triad and faulty thinking). You should be able to explain each and evaluate them, recognising that depression usually results from an interaction of biology and thinking.
What is unipolar depression?
Its characteristics include a persistent low or sad mood, loss of interest or pleasure in activities, low energy and tiredness, changes in sleep and appetite, difficulty concentrating, feelings of worthlessness or guilt, and sometimes thoughts of self-harm. To be diagnosed, symptoms usually last for at least two weeks and interfere with daily life. The "unipolar" label distinguishes it from bipolar disorder, where mood swings between depression and mania.
The influence of genes: Caspi et al. (2003)
This fits the wider view that depression runs in families partly because of inherited differences in brain chemistry, especially serotonin, while life events trigger the disorder in vulnerable people.
The cognitive theory of depression
The cognitive theory (associated with Beck) says depression is caused not by events themselves but by faulty, negative thinking about them. Beck described the negative triad: depressed people hold automatic negative views of the self ("I am worthless"), the world ("everything is against me") and the future ("nothing will improve"). They also show cognitive biases, such as overgeneralising (treating one failure as proof of total failure) and focusing on the negative while ignoring positives. These biased thoughts keep the low mood going in a vicious cycle.
Evaluation. Strength: the cognitive theory leads directly to an effective treatment (cognitive behavioural therapy), and negative thinking patterns are reliably found in depressed people. Weakness: it is not always clear whether negative thinking causes depression or is a symptom of it, and it can seem to blame the person for their illness. The genetic explanation is reductionist (focusing on one gene), and the strongest account combines both.
Try this
Q1. Name the three parts of Beck's negative triad. [3 marks]
- Cue. Negative views of the self, the world and the future.
Q2. Which version of the serotonin-transporter gene did Caspi link to higher depression risk? [1 mark]
- Cue. The short version, after stressful life events.
Q3. Explain one weakness of the cognitive theory of depression. [2 marks]
- Cue. It is unclear whether negative thinking causes depression or is a symptom of it.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20183 marksDescribe the cognitive theory of depression. (Paper 1)Show worked answer →
A 3-mark Describe item rewards the central idea that faulty thinking causes depression, with the negative triad.
The cognitive theory says depression is caused by faulty, negative thinking rather than events themselves. Beck described a negative triad: depressed people hold negative views of themselves (worthless), the world (unfair or hostile) and the future (hopeless). They also show cognitive biases, such as focusing on the negative and overgeneralising from one bad event, which keep the low mood going.
Markers reward faulty negative thinking as the cause, the negative triad (negative views of self, world and future), and the idea that biased thinking maintains depression.
Edexcel 20214 marksExplain how the study by Caspi et al. (2003) supports a role for genes in depression. (Paper 1)Show worked answer →
A 4-mark Explain item rewards linking the study's findings to a genetic influence on depression.
Caspi et al. studied a gene that affects the transport of serotonin, which comes in different versions (alleles). They found that people who had inherited the short version of the gene were more likely to develop depression after stressful life events than people with the long version. This supports a genetic role because the same stressful events produced different outcomes depending on the gene a person had inherited.
Markers reward describing the serotonin-transporter gene and its versions, the finding that the short version raised the risk of depression after stress, and the conclusion that genes influence vulnerability. The strongest answers note this is a gene-environment interaction, not genes alone.
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Sources & how we know this
- Pearson Edexcel GCSE (9-1) Psychology (1PS0) specification — Pearson Edexcel (2017)