Studies into Stress and illness.

Cohen et al (1993)
1. Cohen investigated the effect of stress on the likelihood of developing a common cold.
2. 394 pps completed a questionair on the number of stressful life events they had experienced in the past year
3. They also looked at their degree of stress and level of negative emotions such as depression
4. Pps were exposed to a common cold virus and 82% became infected, failing to fight of the infection was correlated with their stress index scores.
5. Therefore, life stress and negative emotions reduce the effectiveness of our immune system.
Evaluation of Cohen et al (1993)
1. Sample
  1. High population validity due to large sample size of 394 pps, therefore is generalisable to whole population
2. Validity
  1. Low internal validity, due to wanting to measure the function of the immune system with an indirect approach. Instead of measuring actual function they measured the likelihood of developing a cold.
3. Control
  1. High control for standardised proceedure, eg questionaire with same questions, dose of infection, being monitored. This all created reliable and replicable results.
  2. Low control for participant variables as everyone's immune system differs and this cannot be controlled. This extraneous variable will effect results making them less accurate.
4. Reliability
  1. High reliability due to questionnaires, they are easy to repeat and are standardised with the same questions used each time.
Kiecolt-Glaser et al (1984)
1. Focused on naturalistic life stressors such as exams along side measured of immune function
2. 75 medical students preparing for final examinations.
3. Measured their Natural Killer Cell Activity before (to create a baseline) and during the exam period and completed questionnaires on negative life events and social isolation.
4. NK cell activity significantly reduced in high stress samples when compared to low stress samples. Greatest reductions were in those who reported higher levels of social isolation
5. Exam stress (is a brief natural stressor) making people potentially more vulnerable to illness and infections by reducing the immune system
Evaluation of Kiecolt-Glaser et all (1984)
1. Sample
  1. Low population validity, the sample used was small (75) and only contained medical students, therefore it is not generalisable beyond the sample used
2. Validity
  1. High internal validity, the study measures the Natural Killer Cell Activity directly with blood tests and actual immune function is studied. This created valid results
  2. High ecological validity as exams are a part of life that most experience, this makes results generalisable beyond research setting.
3. Control
  1. High control due to taking a sample before and during the exam period, this creates a baseline to compare the results to, reducing the effects of individual differences, increasing the results accuracy and validity

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Studies into Stress and illness.

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