The cognitive vulnerability hypothesis argues that there are maladaptive thinking patterns that make a person more likely to develop a mental illness.  Aaron Beck hypothesized that a pattern of negative schemas about oneself, others, and the future play a key role in Major Depressive Disorder.  These negative thoughts about oneself are seen as stable and global - that is, that they are not likely to change and they affect all areas of one's life. 

Cognitive psychologists have difficulty explaining how this way of thinking leads to depression.  Some argue that negative cognitions lead to stress - about interacting with others or the future.  This stress may then the actual trigger that leads to the disorder. In other words, it may be an example of domino causality - negative cognitions lead to stress, stress leads to genetic expression which may then lead to the disorder.  However, this actual link is not so easy to empirically establish.

Another problem of cognitive psychology is that the majority of their research is correlational in nature. This means that it is difficult to resolve bidirectional ambiguity - that is, it is not clear whether negative cognition leads to depression or whether depression leads to negative patterns of thinking.  Alloy et al were hoping to resolve this question.

Alloy et al used a sample of non-depressed college freshmen with no other diagnosed disorders. Half of the sample had a history of clinical depression; the other half did not.  The students with a history of clinical depression demonstrated no symptoms at the beginning of the study.

To begin, the students were given a test to measure their cognitive style. The students were identified as either High Risk (HR) or Low Risk (LR) for depression based on their thinking patterns.  The researchers carried out follow-up assessments every 6 weeks for 2.5 years and then every 4 months for an additional three years.  The study was based on a combination of questionnaires and structured interviews to identify stressful life events, cognitive style, and symptoms of depression.

The results found that in the group with no prior history of depression, 17% of the HR students developed Major Depressive disorder, compared to only 1% of the LR students. In addition, 29% of the HR group showed symptoms of minor depression, compared to only 6% of the LR group.

Among the group with a past history of depression, 27% of the HR group relapsed, whereas only 6% of the LR group did. In addition, 50% of the HR group showed symptoms associated with depression, compared to 26.5% of the LR group.

In addition, the rate of suicidality was higher in the HR groups (28%) compared to the LR groups (12.6%).

It appears that negative cognitive style played a role in both onset and relapse.

Participants also took a test in which they listened to a list of adjectives.  For each adjective, they were asked whether they thought that the word described them.  At the end of the list, they were asked to recall as many words as possible from the list.  The researchers found that the HR groups showed faster processing and better recall of negative information; and slower processing and worse recall on positive information

• The study used method and data triangulation, increasing the credibility of the findings.

• The tests used to measure cognitive style are highly standardized and have a high level of reliability.

• The use of a pre-test, / post-test design helps to diminish the bidirectional ambiguity.  However, the study is a natural experiment - that is, the researcher does not manipulate the independent variable.  This means that it is not possible to establish a cause and effect relationships.

• The link between cognitive style and depression may be more complex than the study actually proposes.  See the second above about domino causality.

• The theory of cognitive vulnerability has been applied in therapy (CBT) and has been shown to be effective.