Outline and evaluate research into the relationship between the immune system and stress.

Kiecolt-Glaser’s experiment lacks population validity. This is due to the fact participants were not only from the same state in America but also a very specific age range too. This decreases the amount we can generalise the findings to the rest of the population. This is because Americans may have better immune systems than people in different countries, or because they were students, they could therefore naturally have experienced more stress recently or have more stressful lives due to the nature of university life. However, in order to try resolve this issue Kiecolt-Glazer carried out two more pieces of research, one in 1987 on Alzheimer’s patients and another in 1987 on participants going through divorce. It was found that the results were very similar even when using different participants going through different forms of stress, which not only increases the reliability of the research but also increases its population validity.

One limitation of Kiecolt-Glazer’s research is that it is a correlational study. Due to this it can only be concluded that there is a link between stress and a suppression of immune system. No cause and effect cam therefore be established without the knowledge of a mechanical system because there is the possibility that there is another factor that effects both sets of data.

Being a natural experiment Kiecolt-Glaser’s experiment has low internal validity, due to the fact the lack of experimental manipulation. This is because with practically no control of variables it is exceedingly difficult to identify what extraneous variables could have influenced the findings. Yet Kiecolt-Glazer’s research did decreases the likelihood of demand characteristics due to the fact an objective measure of immune system was used; blood samples to show natural killer cell levels. In doing the research does gain some internal validity. Kiecolt-Glaser was also able to compare levels of natural killer cells at two different times, due to taking two samples of blood with the first acting as a baseline. This baseline took the individual differences of the participants’ immune system into account, increasing the internal validity further.

In addition to this, Kiecolt-Glaser used two well established scales of loneliness and stressful life events, namely The Social Readjustment Rating Scale and the ICLA Loneliness scale. This not only increases the credibility of the findings but also allowed each participant to be easily compared to one another.

The reliability of the study increases due to the experiment by Cohen et al yielding similar results. Cohen et al asked participants to complete questionnaires assessing stressful life events, perceived stress and negative effects. Following this 394 healthy participants were then exposed intentionally to a common cold virus and were monitored whilst in quarantine for the development of clinical illness. The results were consistent with Kiecolt-Glazer as the higher scores on each of the 3 stress scales were associated with a greater risk of getting a cold.