Equifinality (Barlow, & Durand, 2005) is a term that describes the same end product resulting from possibly different causes. Just as there may be many reasons for headache, there may also be a variety of reasons for depression. Leading contemporary psychologists agree that aetiology of depression could not possibly be explained by only one set of factors, being it biological, psychological or social, whatever the precipitating factor.

Biological aetiological factors involve genetic, neurochemical and hormonal factors.

Studies that allow estimation of genetic contribution are family studies and twins studies. Family studies show that the rate in first degree relatives of individuals with mood disorder is consistently about two to three times greater than in families without depressed members. Similarly, twin studies show that concordance rate in co-occurrence of depression is far greater within identical twins population than is within fraternal twins (McGuffin, Rijsdijk, Andrew, Sham, Katz, & Cardno, 2003).

Research on abnormal brain functions associated with depression has focused on deficient availability of a class of neurotransmitters known as dopamine and serotonin (Hansell, & Damour, 2005). The hormonal system in the body may also play an important role in some forms of depression. For a long time, clinicians have known that endocrine disorders such as hyperthyroidism or hypothyroidism can cause depression.

Psychological aetiological factors contribute to the development of depression in 60 to 80% of cases (Barlow, & Durand, 2005). Furthermore, most of these psychological experiences are unique to the individual. Main factors could be allocated into three clusters – stressful life events, learned helplessness and negative cognitive styles.
 
Stress and trauma are among the most striking factors in developing of all psychological disorders. This is reflected in wide adoption of the diathesis-stress aetiological model that describes genetic predisposition and psychological vulnerability. Predisposition (diathesis) is triggered by stressful event and might lead to depression. Reaction to stressful event or trauma is an individual response.

It means that not all persons exposed to the same stress will develop psychological disorders. It is called multiple causality. Having a particular vulnerability does not mean that a person will develop an associated disorder. The smaller the vulnerability, the greater stress is required and conversely, the greater the vulnerability, the less stress is required. This model of nature – nurture interaction has been very popular, although here presented in a simplified form.

Seligman (1975) presented interesting research findings with animals. Dogs and rats have an emotional reaction to events over which they do not have control. Animals learn that nothing they do helps them avoid a shock (from experiment) and soon they become very helpless, give up and display animals’ equivalent of depression. Seligman suggested that humans behave similarly – they tend to decide that they have no control over the stress in their life and become depressed. These findings evolved into an important model called the learned helplessness theory of depression (Barlow, & Durand, 2005).

Aaron Beck (1967) suggested that the depression may result from a tendency of persons to interpret everyday events in a negative way and he called it the negative cognitive style. People with depression make the worst of everything and make cognitive errors about themselves, world around them and their future. Beck called it depressive cognitive triad.

Most prominent social aetiological factors in developing depression are marital relationship, gender and social support. World data on depression shows a dramatic gender imbalance where almost 70% of individuals with depression are woman.

Diagram 1
Lifetime international rate per 100 people for major depression
(Source: Barlow, D.H., & Durand, V.M. (2005). Abnormal psychology: An integrative approach. Belmont, CA: Thomson Wadsworth)

As presented in the image below, an integrative model of depression’s aetiology would necessary take into account all factors that contribute to the development of depression. The interplay between biological and psychological vulnerability, and presence of stressful life events could activate stress hormones; create sense of hopelessness and cognitive distortions. It may be the base for problems in social and intimate relationships and this process often leads to depression.   

Diagram 2
An Integrative Model of Mood Disorders
(Adapted from: Barlow, D.H., & Durand, V.M. (2005). Abnormal psychology: An integrative approach. Belmont, CA: Thomson Wadsworth)

Source: www.counsellingacademy.com.au

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