Caspi (Psychological problems)
Caspi et al. (2003) Influence of Life Stress on Depression (textbook pg.72-73) “Understand the aims, procedures and findings (results and conclusions), strengths and weaknesses of”
Background: We know that stressful life events can cause depression – but not everyone who experiences stressful life events becomes depressed. Caspi investigated a gene (5HTT) that controls serotonin, which can make some people more likely to become depressed after life events. If low serotonin causes depression, then we can treat depression using antidepressant drugs like SSRIs which aim to increase levels of serotonin in the brain and improve mood.
| A | Caspi aimed to investigate why stressful life events lead to depression in some people and not others. Caspi aimed to investigate whether people with a short copy of the 5HTT gene are more likely to have depression after a stressful life event. |
| P | SAMPLE: 847 participants took part: Some of them (17%) had two copies of the short version of 5HTT. Some of them (51%) had one copy of the short version of 5HTT. Some of them (31%) had two copies of the long version of 5HTT (no short copy). LONGITUDINAL STUDY: The study was longitudinal, which means they studied the same participants over a long period of time (5 years). QUESTIONNAIRE 1: Each participant completed a questionnaire about life events between their 21st and 26th birthdays, e.g. problems with money, health or relationships. QUESTIONNAIRE 2: Each participant completed a questionnaire to assess symptoms of depression – completed in the year before their 26th birthday – each participant was given a numerical “depression score” based on their answers. |
| R | Those with a short copy of 5HTT who experienced stressful life events were more likely to have depression than those with two long copies of 5HTT. Those with a short copy of 5HTT were more likely to have suicidal thoughts after stressful life events compared to those with just long copies of 5HTT. Those with two short copies of 5HTT were the most likely to have severe depression symptoms if they had stressful life events. |
| C | There seems to be an interaction between life events and genetic factors (short copy of the 5HTT gene). This supports the diathesis-stress model of depression, that you need a genetic pre disposition and environmental trigger. This means both nature (biology) and nurture (environment) contribute to unipolar depression. |
| G | (+) They used a large sample size of 847 individuals, meaning the results about 5HTT causing depression can generalise back to the target population. |
| R | (+) A standardised procedure was used (e.g. the same questionnaires assessing depression and life events) meaning the procedure can easily be replicated to check the consistency of results, to test for reliability. |
| A | (+) The results are useful because they provide supporting evidence for the genetic theory and diathesis stress models for explaining depression. If we know that depression is caused in part by 5HTT which controls serotonin release, we can treat depression using antidepressants that increase serotonin levels, like SSRIs. |
| V | (-) The participants gave self-report data through questionnaires which could lack validity, as they might not talk about their behaviour accurately. For example, some people may “down play” their symptoms as they don’t want to make a fuss, whereas other people may over exaggerate. The data might not be accurate. (+) The researchers gave each participant a depression score based on their symptom questionnaire responses. This gives quantitative data which is objective – everyone will interpret the score the same and it isn’t prone to opinion. |
| E | (-) It might be upsetting (and cause psychological harm) for participants to answer questionnaires about their stressful life events. Reliving these memories could be traumatic, particularly for those participants who did experience depression. |
Caspi’s Study Key Term Glossary
| Serotonin | Neurotransmitter that controls mood (high levels = happiness, low levels = depression) |
| 5HTT gene | A gene that controls the amount of serotonin available. If we have a short copy of the gene, we have less serotonin |
| Longitudinal | A study that takes place over a long period of time – the same participants are used throughout the study |
| Diathesis stress model | A theory suggesting behaviour is caused by an interaction between a genetic pre-disposition and environmental triggers |
| Symptoms | Behaviours, thoughts or feelings that someone is experiencing that can be used to help form a diagnosis |
| SSRIs | Antidepressant drugs that increase the amount of serotonin in the brain to improve mood |
| Nature | Biological factors e.g. genes and brain function |
| Nurture | Environmental factors such as upbringing and life events |
| Need more help? Want to stretch your understanding? Need a video example? |
| https://tuxfordpsychology91.wordpress.com/2-clinical-psychology/ https://www.tutor2u.net/psychology/reference/caspi-2003 |
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