RESEARCH INTO THE EFFECTS OF STRESS ON THE IMMUNE SYSTEM
KIECOLT-GLASER ET AL 1993

natural experiment
stress of exams affect immune system
75 medical students preparing for final exams
blood samples taken 1 month prior to final exam
bloods taken again during the exam period
measured the activity of the natural killers in the blood samples
students also filled out a questionnaire to assess any psychological variables
e.g. life events and loneliness
significant reduction of natural killer cells in second sample
due to first sample stress=suppressed immune system
greatest reduction in sample 1 for students reporting high levels of social isolation/loneliness
concluded natural stressers reduce

+ high external validity as it was a natural experiment, the stress experienced was real and will affect others who may take exams in a similar fashion.
- a restricted sample as they were doctors in their final year, they may have learnt to deal with stress. we cannot assume therefore that stress affects everyone's immune function in the same way.

COHEN ET AL 1993

394 participants
completed questionnaire on stressful life events in past year
rated their stress levels and negative emotions
stress index created from 3 scores, ranged from 3-12
participants exposed to one of fie cold viruses
administered through nasal drops
diagnosed after 7 days by a doctor
number of participants who developed colds was recorded
all showed signs of infection
82% developed a cold
direct link between stress and illness
those scoring highly on stress index most likely to develop the cold

+high internal validity due to controlled variables such as age, weight and smoking etc. meaning we can be more certain that the development of the cold was less likely to be due to factors other than stress

-unclear cause and effect relationship and so cannot be sure that immune function is affected by stress levels. e.g. does being stressed lead to illness or does illness lead to stress. a cyclic process?

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RESEARCH BY KIECOLT-GLASER ET AL 1993. AQA

RESEARCH INTO THE EFFECTS OF STRESS ON THE IMMUNE SYSTEM