Physiological Psychology: 2

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Physiological Psychology: Stress

APFCC Key Studies

Independent Variable: The manipulated variable; the variable that is changed on purpose in an experiment.

Dependant Variable: The responding variable; the variable that may change as a result of a change in the independent variable.

Kiecolt-Glaser et al


  • To discover a link between stress and reduce immune function.
  • They aimed to establish a difference between conditions of high and low stress.
  • They also wanted to see whether other factors such as psychiatric symptoms, loneliness and life events were associated with immune function.


  • A total of 75 first year medical students, it was a self selected sample.
  • This was a natural experiment because the independent variable, (the level of stress due to the imminence of exams) was naturally occurring.
  • A blood sample was taken a month before their exams (a low stress condition) and also on the first day of their final exams (a high stress condition).
  • The measurement of natural killer cells and T cells was taken as indicators of immune function (the dependant variable).
  • On both occasions, the students were given a questionnaire measuring psychiatric symptoms, loneliness and life events.


  • Natural killer and T cell activity declined between the low-stress and high stress conditions. Thus, the assumption was correct.
  • The questionnaires revealed that immune system responses were particularly suppressed in participants who reported that they were experiencing psychiatric symptoms, loneliness, or stressful life events.
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  • Stress is associated with suppression of the immune system and the effect is stronger when there are more sources of stress.
  • Only associations were established. Implications include the importance of stress management to good immune functioning.


  • The independent variable was not under the control of the experimenter and as a result, cause and effect cannot be inferred as the independent variable is neither controlled or isolated.
  • The functioning of nearly all the medical students was within the normal range.
  • The immune system is very complicated and so ...

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