The Interactionist Approach

• The diathesis-stress model is based on an holistic approach to explaining and treating a range of disorders, including depression and schizophrenia
• The diathesis-stress model assumes that schizophrenia does not stem from one main source but is instead a combination and interaction of biological, psychological and social factors
• The model suggests that an individual may have a vulnerability/predisposition (usually biological but not necessarily so) to develop/worsen schizophrenia (known as the ‘diathesis’) which is triggered by a stressful event or situation (usually psychological/social but not necessarily so)
• The original diathesis-stress model (Meehl, 1962) posits that the diathesis is entirely genetic and it is situational stressors that work to bring about the illness or to intensify symptoms of the existing illness
• The more vulnerable a person is (i.e. the higher their diathesis) then the less stress is needed to ‘pull the trigger’ as it were, ergo something that may seem trivial to a low-diathesis person could prove intolerable to a high-diathesis person
• The diathesis-stress model has undergone some revision and modification since its early inception in the 1960s: 
  • Diathesis may come in many forms: biological (e.g. specific genes which predispose a person to schizophrenia); psycho-social (e.g. early experience of abuse or bereavement)
  • Stress may also come in many forms and may form the basis of the diathesis rather than being the trigger (e.g. living with a parent who has a mental illness)
  • Recent research has suggested a neural diathesis-stress model of schizophrenia which proposes that stress heightens cortisol levels and that this triggers/worsens the symptoms of schizophrenia (Jones & Fernyhough, 2007)
• Protective factors in someone’s life may guard against the potential harm of the various risk factors that could trigger schizophrenia:
  • The risk factor of toxic parenting could be offset by having caring grandparents who offer the love and nurture a child needs
  • Personal traits such as resilience, optimism, stoicism can also help to protect a vulnerable individual
  • Protective factors may highlight why person A with roughly the same diathesis/stress in their life as person B has, does not develop schizophrenia while person B does succumb to the illness

Is stress the trigger or the starting-point of a schizophrenic episode?

Research which investigates the interactionist approach

• Pruessner et al. (2017) - A review article focusing on the neural diathesis-stress model in light of a more sophisticated understanding of the role of the hypothalamic-pituitary-adrenal (HPA) system in a wider neurobiological context including the effect of early stress on brain structure and development 
• Silverton (1988) found that a sample of participants who had schizophrenic parents were more likely to develop schizophrenia and to engage in criminal behaviour if they had shown short attention spans as infants which supports the original diathesis-stress model (i.e. some people may have a genetic vulnerability to schizophrenia which is marked by distinct behaviours in early childhood)
• Walker et al. (1989) - Families in which there was parental mental illness and mistreatment of children were more likely to produce children that showed increasingly schizophrenic behaviours and symptoms

Evaluation of the interactionist approach

Strengths

• Research such as Tienari (2004) lends strong support to the model as it highlights the interplay between biological and psycho-social factors in the development of schizophrenia which means that the model has good validity
• The model could be applied to form intervention strategies such as resilience-building, mentoring/buddy programmes, social skills training so to this extent it has some external validity

Weaknesses

• The model has been criticised for not acknowledging the role of other biological factors such as the role of neurotransmitters (see the dopamine hypothesis for example) in the development of schizophrenia which means that it may offer only a partial explanation
• There is some vagueness over exactly how biological, psychological and social factors interact according to the model which means that it lacks objectivity i.e. it is not scientific or reliable

Link to Issues & Debates:

The diathesis-stress model strives to be holistic rather than reductionist in its all-encompassing explanation of how a disorder such as schizophrenia develops. It achieves this holistic aim to some extent but it still cannot fully account for individual differences which means that it is not fully holistic and may lack some explanatory power.