Kiecolt-Glaser et al. (1984) conducted a natural experiment on medical students that investigated whether the short-term stressor of approaching exams had an effect on the immune system functioning. They took blood samples of the 75 participants one month before their final exams and then again on the first day of exams. The blood samples were then analysed for leucocyte activity of the natural killer cell. Questionnaires were also given to establish the students’ psychiatric mind set and their life events. They found that the natural killer cell activity decreased in the second blood sample, compared with the first. Furthermore, immune response was particularly low for those who scored highly in the loneliness, psychiatric symptoms and stressful life events symptoms. They concluded that stress is associated with reduced immune system function.

Another piece of research was conducted by Kiecolt-Glaser et al. (2005) but this time investigated long-term, chronic stress. They tested the impact of interpersonal conflict on wound healing. They found that blister wounds on the arms of married couples healed more slowly after the couples had had discussions which were conflicting rather than supportive.

A key strength of Kiecolt-Glaser’s short-term stress study is that it contained stressors that were naturally occurring, which increases validity because it creates more mundane realism as the stressors, IV and DV weren’t artificially induced. Furthermore, another strength is that participant variables were controlled because the students were compared with themselves, this increases internal validity.

A limitation of her medical student study is that the sample was medical students who had volunteered, they were only from one subject area and there was more males (49) compared with the 26 females. This means the sample could be biased to a certain gender and it’s