- This is most evident in patient samples compared to community samples. This might be explained by the fact that in community samples patients aren't experiencing clinical depression or patients in community samples may contain individuals with less episodes in the recurrence group compared to patient samples.
- As the mean age of a patient sample increases the recurrences of depression will be more easily initiated without severe stressful life events compared to first episodes. They will be more likely be precipitated by severe life events.
- With more women in a sample it is likely that a recurrence will be precipitated by a severe stressful life event. Women are more likely than men to experience a severe stressful life event both before first episodes and before recurrences.
It is asserted that the first episode of a depression is more likely to be preceded by major psychological stressors than are subsequent episodes. This was proposed by R. Post a well known researcher and psychiatrist specialized in bipolar disorder. This ia also known as the kindling phenomenon. In clinical practice it is observed that less and less stressful life events elicit depression across the course of the disorder. But these observations are biased since it is done on a selection of patients.
Recent studies have investigated the differential prediction by life stress of a first onset versus a recurrence. The well known odds ratio is used in these studies. According to a recent review comparing odds ratios has it's disadvantages. They did a systematic review with a new statistical method, using one statistical index to compare first episodes with recurrent episodes and triggering life events. They also looked at moderators such as age, gender and patient status.
Their literature search yielded 28 studies of which 13 could be included in their final sample for analysis.
They used published, unpublished studies, and dissertations. They excluded bipolar disorder. This theory was first used and researched for bipolar disorder as such, so manic and depressive states were included. This review includes only unipolar depression.
Overall their result provide support for the hypothesis that recurrence of depression is precipitated by less severe stressful life events. 11% more individuals in the first onset group than in the recurrence group experienced a severe stressful life event. The clinical significance of this small percentages is unclear. It doesn't explain all the variance in the stress-depression relationship. It may be only applicable to certain groups of individuals or under certain conditions. One group I can think of are the more severe depressed patients, psychotic depressed patients or inpatients. Just stressful life events alone doesn't explain the recurrence of depression.
The most important limitation of this systematic review is the small number of studies (n=13) and the probable sample overlap.
Overall conclusion is that in some patients recurrence of depression might be precipitated by lesser severe stressful life events compared to the first and previous episodes. Further research is needed into which patients and what other factors moderate this effect and what other factors contribute to recurrence.
Stroud, C.B., Davila, J., Moyer, A. (2008). The relationship between stress and depression in first onsets versus recurrences: A meta-analytic review.. Journal of Abnormal Psychology, 117(1), 206-213. DOI: 10.1037/0021-843X.117.1.206