There is evidence to suggest acute stressors can cause suppression of the immune system and decrease immune cell functioning. The study by Kiecolt-Glaser et al. (1984) investigated whether the stress of taking exams caused a change in the amount of white blood cells in the blood. Kiecolt-Glaser studied 49 male and 26 female first year medical students at the Ohio State University College of Medicine in a natural experiment. The students had blood taken a month before their exams, a period of relatively low stress and on the day of their first exam, a highly stressful day.
The students had volunteered to take part and a repeated measures design was used. The amount of stress the students felt they were under was determined by a series of questionnaires such as the SRRS devised by Holmes and Rahe which explored topics such as recent life events and psychiatric symptoms and loneliness. The students’ immune functioning was assessed by measuring the quantity of white blood cells in the blood. She found that the blood sample taken a month before the exams had a higher white blood cell count compared to the samples taken on the day of the exam.
Also, immune responses were particularly weak in those who reported experiencing stressful life events, psychiatric symptoms such as depression or anxiety, and loneliness. It can be concluded that stressful experiences such as exams reduce the effectiveness of our immune system. Therefore it could be said that periods of stress mean that you are more likely to be ill. There are many evaluation points that can be made for this study. This was a natural experiment when the naturally occurring exams were taken advantage of, rather than replicating a stressful event.
This means that situations and their effect on the body can be studied where it would be unethical to cause stress artificially. Natural experiments also have a high ecological validity. Taking exams is an event that every student experiences and so that the stress felt would be naturally occurring in real life. However, natural experiments only show a correlation. It cannot be concluded from the results that the exam stress caused the decrease in white blood cells.
In natural experiments the independent variable, the stress, cannot be controlled and the dependent variable, the amount of white blood cells, may have been influenced by other factors such as their general health, diet, physical activity, sleep pattern and medication. Also, some people may feel more stressed than others about sitting exams. It can be argued that personality differences determine susceptibility to stress and how well people can cope with it. The students’ coping behaviours may have an effect on their white blood cell quantity such as drinking alcohol, smoking or taking recreational drugs.
Questionnaires were used to measure the amount of stress each participant experienced. Questionnaires are a self report measure that can be used to collect large amounts of quantitative data and is relatively cheap and quick compared to other measures such as interviews. They also allow participants to inform the researcher of issues they may feel uncomfortable talking about face to face. Answers can be easily analysed when closed questions are asked. However, questionnaires may be interpreted incorrectly by participants and may be subjective.
Participants may answer the questions according to how they want to be viewed by others and may not answer truthfully. Questionnaires are often retrospective, and the participants may have difficulty recalling events that happened in the past. The sample size was small and of a particular group of people. A small sample size means that it is difficult to generalise the results and it means that the conclusions have less population validity. The participants were all American university students who volunteered for the study.
The main advantage volunteer sampling is that it can be comfortably assumed that the participants are willing to cooperate in the study. However it can be argued that volunteer sampling only attracts a certain kind of person. As the study only focused on American university students it has little population validity. As all of the participants were young, it is difficult to generalise the findings beyond that age group and may not have been representative of those who don’t take exams regularly and of a different age group.
By using a repeated measures design, using the same participants for both manipulations, the researcher could exclude the effects of individual differences that may occur in an independent groups design. These designs require fewer participants and it is easier than finding other participants or matching participants with a matched pairs design. However, having to have 2 injections may have caused the students to feel nervous and increase the already considerable amounts of stress that they were suffering and they may have felt that they are wasting time that they could use studying for their upcoming exams.