Caspi 2003: Life Stress and Depression

Aims

To investigate why stressful life events seem to lead to depression in some people and not others

Who were the participents?

Participants were members of the Dunedin Multidisciplinary Health and Developmental Study – a group of children who have been studied since birth. 

Aproximatley how many people took part and how many groups were they split into?

In total, 847 children took part.  They were divided into three groups based on the version of the 5-HTT gene they had:

What version of the HTT-5 gene did group 1 have?

Two copies of the short version of the gene

What version of the HTT-5 gene did group 2 have?

One copy of the short version and one copy of the long version of the gene

What version of the HTT-5 gene did group 3 have?

Two copies of the long version of the gene

What kind of study was this?

This was a longitudinal study (over years), with each participant completing a questionnaire that measured the life events that occurred between their 21^st and 25^th birthdays. 

Results

1. Participants who were found to have at least one short version of the 5-HTT gene and who had been through stressful life events between the ages of 21 and 26 years old showed a significant increase in symptoms of depression after the event and up until they were 26 years old. They were more likely to be diagnosed with depression than participants with two long versions of the gene.

• Those with a short version of the gene were more likely to develop suicidal thoughts after stressful life events than those with two long versions of the gene.

• Those with two short versions of the 5-HTT gene were most likely to report severe depressive symptoms if they had suffered a number of stressful life events, [including a significantly higher report of suicidal thoughts or attempts if they had faced more than three stressful life events.]

Conclusion to the study

The evidence seems to suggest that there is an interaction between life events and genetic influences in causing depression.  This suggests that both nature and nurture work together to increase the likelihood of a person developing depression. 

Give two strengths of this study

• One strength of the study is the size of the sample.  For example, there were 847 participants, which is a large sample. This is a strength because it means that generalising the results from the study should be easier that if the sample had been very small.

• Another strength is that the information from this study could be useful for doctors as it tells them that someone with depression could have different causes for their symptoms. For example, doctors should look at a variety of factors in their patients, including whether they have been through stressful events and whether they have the short version of the 5-HTT gene, to understand why they have become depressed.  This is a strength because it might also help them to understand why some people become depressed after a life event, while others don’t.  Realistically, however, doctors find it very difficult to assess all possible causes of a person’s depression due to time and cost restraints.

Give two weaknesses of this study

• One weakness of the study is that the researchers thought there was a chance that some people were naturally more likely to put themselves in situation where stressful life events might happen.  For example, the short version of the 5-HTT gene might be a natural factor that makes people prone to situations that are stressful.  This is a weakness because the gene and life events may not be causing depression as such, but instead the person is in more stressful situation s that could cause depression.

• Another weakness is that the evidence from the questionnaires is self-report data.  For example, some people might exaggerate their symptoms of depression while others might not want to make a big deal of them.  This is a weakness because their answers may not be true (lack of validity) and can't be considered reliable (consistent every time).