Rahe et al. (1970) Aims

Transcription

1 Rahe et al. (1970) Aims This study aimed to investigate the relationship between stress caused by life events and the incidence of subsequent illness. The study also aimed to extend previous research in the field of stress and illness in two particular ways. Firstly, other studies used participants who were hospital patients hence Rahe et al. wanted to investigate stress and illness in participants who were not clinical patients. Secondly, previous studies had relied on retrospective reporting of illness. One problem with this type of reporting is that recall is vulnerable to memory errors. Rahe et al. therefore wanted to overcome the potential bias of retrospective studies by conducting a prospective study. Context One of the first researchers to investigate the concept of stress was Walter Cannon. In the early 20 th century Cannon showed that when the sympathetic nervous system is activated by a stressful event, certain biological changes occur, e.g., increased heart and respiration rates. These responses prepare us to tackle the stressor or to escape it. Cannon called this the fight or flight response. The understanding of the biological nature of stress was furthered by the work of Hans Selye. In the 1920s Selye began research into how the body deals with stressful events and showed that certain hormones such as adrenaline were vital in responding to stress. He also realised that if a stressor is not quickly removed and becomes long lasting, the body s stress hormones start to deplete and illness can result. However, research in the 1960s by Meyer Friedman and Ray Rosenman showed that personality plays a role in stress and illness. Their research indicated that people who become easily stressed as a result of being competitive, working against the clock, and being self-critical are more vulnerable to heart disease than people who adopt a more relaxed attitude to life. Other researchers in the 1960s sought to establish whether the amount of stress that a person is suffering from could be accurately measured. In 1967 Thomas Holmes and Richard Rahe said that the life events that we need to deal with cause us stress. Some examples of life events are marriage, Christmas, passing an exam, and bereavement. Holmes and Rahe also thought that because life events vary in severity, some life events will be more stressful than others. Therefore the amount of stress a person is suffering at any point in time will depend on the number and type of events being experienced. However, before the degree of stress can be measured, life events need to be classified in terms of the degree of stress they produce. To do this, Holmes and Rahe analysed the medical records of 5000 patients and produced a list of 43 life events that seemed prevalent before the onset of illness. They then recruited 100 participants to judge the psychological impact of each event. This information was used to compile the Social Readjustment Rating Scale (SRRS). In the SRRS the judgements were ordered on an arbitrary scale of The death of a spouse was judged to have the highest

2 psychological impact and this event was assigned a numerical value of 100. The impact values used for the life events are known as life change units and the degree of stress a person has experienced in a certain period can be calculated by adding up their total life change units to produce a life change unit score (LCU score). A modified version of the SRRS was used in Rahe et al. s study to investigate whether stress is related to the onset of subsequent illness. Procedure The participants were 2684 male U.S. Navy personnel serving on board three U.S. Navy cruisers. Their mean age was 22.3 years. Two thirds of the sample were high school graduates and the range of service across the sample varied from a few years service to over 30 years of service. One ship was operational in the Mediterranean for its tour of duty and the other two ships were involved in military operations off the Vietnam coast. Prior to embarking on tours of duty (6-8 months in length), the sailors filled in a questionnaire called the Schedule of Recent Experience (SRE). This was designed to assess the life events experienced by the sailors in the two years before their tours began. The sailors completed a military version of the SRE and this included questions about life events in various areas of the sailors lives, e.g., personal, occupational, religious areas. Each life event was given an LCU value so that an LCU score was obtained for each sailor. In order to help reduce any bias in their answers, the sailors were not told that their life event score was going to be correlated with any illness they might experience on board their ships. In addition, the medical personnel on the ships were not given any details about the design of the research. This again served to reduce potential bias. When the tours of duty were completed, the ships medical records were examined for all new reports of illness that had taken place during these tours. Information from these records included the number, type and severity of new illnesses. Findings Prior to analysis, the sailors life change scores for the two-year period were divided up to cover four six-month periods. Therefore, each sailor had four LCU total scores. Pearson product-moment correlations between the total number of cruise illnesses reported by each sailor and each of the LCU scores for the four time periods were then calculated. The result of this analysis was a significant positive correlation between illness and life events in the six-month period immediately before the tours of duty (r = 0.118). The remaining three correlations between the total number of cruise illnesses reported by each sailor and LCU scores in the other time periods were not significant. These results showed that as life event scores rose, there was an increased likelihood that sailors would experience illness on their tours of duty. In addition, this result was only relevant in the six months before the tours.

3 Rahe et al. also conducted further analyses using the LCU scores obtained in the sixmonth period before the tours and the illness data. First of all, they ordered the participants in terms of their LCU score, i.e., lowest to highest, and then divided the participants into ten bands. Each band contained one tenth of the total number of sailors. Therefore band 1, for example, contained 10% of the total number of sailors and was the band with the lowest LCU scores. This part of the analysis showed that the illness rate was lowest around bands 1 and 2 and highest around bands 9 and 10 and provides further support for the positive relationship between LCU scores and subsequent illness. The analysis was then further subdivided according to cruiser. This extended analysis looked at the differences between the bands on each cruiser and found that the percentage increases in illness rates between the lower and higher LCU bands was larger for cruisers 1 and 3 compared to cruiser 2. This shows that the relationship between LCU scores and illness rates was greater on cruisers 1 and 3. Conclusions The general conclusion for this study is that there was a positive relationship between the number of life events experienced by the sailors and the rates of illness reported whilst the sailors were on their tours of duty. In other words, the number of life events experienced increased the likelihood that the sailors would suffer stress-related health problems. However, this conclusion needs to be interpreted with caution because the correlation, although significant, was still low. This means that other factors besides life events could have been exerting an influence on the likelihood of illness. For example, biological factors such as the innate strength of each sailor s immune system could have been influential. As well as biological factors, personality factors could also have played a role. As mentioned previously, research carried out in the 1960s by Friedman and Rosenman showed that vulnerability to illness could be decreased if a person has a more relaxed personality. Therefore, the sailors personality in this study could also have contributed to the lower correlation. Another conclusion that can be drawn is that the different tours of duty undertaken by the three cruisers had some effect on the results. Cruiser 2 experienced the most arduous cruise whilst on its tour of duty and this could have raised stress levels and hence illness rates in the crew. This possibly masked the effects of previous life events on illness levels and this was reflected in the observation that cruiser 2 had a lower percentage increase in illness rate between the lower and higher LCU bands than cruisers 1 and 3. Evaluation A weakness of the correlational method used by Rahe et al. is that you cannot infer cause and effect. In other words, you cannot say that one variable causes a change in another variable. In the context of Rahe et al. s study, it is not possible to say that the

4 stress caused by life events will cause an increase in sailors illness rates when they are on tours of duty. We can only conclude that stress and illness appear to be related in this group, especially as there was no investigation of any other critical factors that could, besides stress, have had an effect on illness levels. Therefore a correlation merely indicates a relationship between two variables and does not take into account the influence of other variables on either of these. Given that the study only used male US navy personnel as participants, there are problems regarding generalisation of the results to other groups of people. This therefore means that the study is low in population validity. For example, would similar results be obtained with female US navy personnel? Or in people who are not in the military? The results of the study therefore need to be interpreted with care because only a very small section of the world s population was used in the sampling. Criticisms can also be made about the SRE that was used to obtain LCU total scores. One problem is that in questionnaires such as the SRE each life event is given a certain value that reflects its psychological impact. However, it is likely that life events will vary in terms of their impact on each individual. For example, an event like Christmas could be stressful for some people but relaxing for others yet its LCU score would not reflect this. As a result the LCU scores obtained in the study may not give a true picture of the stress levels experienced by sailors prior to their tours of duty. This therefore reduces the internal validity of the study. The study can also be criticised in terms of ethical issues. The major ethical issue in the study was that the participants were not told that the results of the life events questionnaire would be correlated with their illness rates. This deception meant that the participants were not able to give informed consent and were not able to withdraw from the study. Furthermore, the medical teams on board the cruisers were not told about the objectives of the research hence they too were also deceived by the researchers. Nevertheless, the deception strengthened the study in that the procedure helped to avoid problems such as participants guessing the aim of the study. A further strength of the study was that the environments the sailors lived in would have kept certain factors relatively constant. For example, the sailors ate similar food, were fit to carry out their duties, and they all worked in the same type of environment. This served to reduce the possibility that other factors could have influenced the levels of illness experienced by the sailors. In contrast, a study investigating the relationship between stress and illness using participants from a more general population would have introduced more variables into the research. However, there was some variation between the crews in that one of the cruisers was not involved in active military operations. In addition, the cruisers were not all deployed to the same location. Therefore, variation in location and duties could have introduced additional variables besides stress and illness and these could have had an impact on the results.

5 Complementary and alternative studies Research into the relationship between stress and illness in US naval military personnel was also carried out by Rubin, Gunderson and Arthur (1972). The participants in this study were 121 naval pilots serving on an aircraft carrier during a six month tour of duty off the Vietnam coast. The participants completed an SRE relating to the 18 month period prior to the tour of duty and illness records were kept by flight surgeons for the duration of the trip. The results were highly similar to those obtained by Rahe et al. in that there was a positive relationship between illness and life events. More recent research by Kiecolt-Glaser et al. (1995) has shown that chronic stress suppresses immune system function and this can slow down wound healing. This study assessed 13 American women who were caring for relatives with senile dementia. The degree of stress suffered by the women was assessed using a stress scale and immune system function was assessed by a blood test and by measuring the amount of time it took for a small wound to heal. The wound was given by a nurse and involved participants undergoing a punch biopsy below the elbow. The results showed that immune function was most impaired in participants suffering high stress levels. This study is therefore further evidence that stress can impair the body s health. Other research, however, has indicated that stress is not necessarily a factor in the onset of some illnesses. A study by Protheroe et al. (1999) investigated the relationship between life events and breast cancer. The participants in this research were 332 British women attending NHS breast clinics. Each woman was asked to complete a life events questionnaire to assess the degree of stress they had suffered in the previous five years. The study found no relationship between stress caused by life events and the onset of breast cancer. Thus this research illustrates that other factors apart from stress could be more critical in the development of certain illnesses. Rahe, R.H., Mahan, J. and Arthur, R. (1970) Prediction of near-future health change from subjects preceding life changes Journal of Psychosomatic Research, 14,