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Although the main focus of this project has been the psychological variables, demographic factors were also explored to determine whether these have any influence over the decision to have a test. Factors with significant associations with intention were entered into the regression analysis. Family history was significantly associated with the intention to have a genetic test, with people at higher risk intending to have the test more than people do at lower risk. Family history is correlated with perceived susceptibility, and this is likely to explain much of this finding, as those who are more at risk may perceive themselves as more susceptible than those who have a less strong family history.

Chapter 4:Psychosocial Aspects of Genetic Testing For Colon Cancer Asymptomatic Individuals with a Family History genetic test were older age and having a larger number of children. It may be that with increasing age the advantages and disadvantages of testing become less important, having a test becomes a matter of personal choice whether to know. Being older has been found to be associated with higher intent in another study of colon cancer (Glanz et al 1999), but in breast/ ovarian cancer, being younger is more predictive of high intent (Lerman et al 1994; Lerman et al 1997; Tambor et al 1997; Meijers-Heijboor et al 2000).

Time of life was also an influence for other participants who were more likely to have a genetic test if they had children. This means that either people who don’t have children are delaying knowing until they do (or are just not interested), or people who do have children are more motivated to have the test. It is not possible in a cross-sectional study to determine which of these possibilities is correct, however it does indicate that knowing for another generation is likely to be an important factor in deciding to have a genetic test. This concern about family indicates that a systemic approach to the issue of intent may be required, looking not only at individuals’ attitudes and cognitions, but the potential impact of the decision on other people and other factors (Kessler & Bloch 1989). It is also not known whether it is actually of benefit for children to leam of their parent’s risk, without first choosing to know themselves. A systemic approach would examine the impact of these decisions on other family members, who themselves may or may not want to know.

Gender was not found to be associated with intent to have a genetic test, this is contrary to the findings of Lerman et al (1996) and Petersen et al (1999) but concurs with the findings of Glanz et al (1999). One possible reason for the lack of influence of gender on intent in this study is a sampling bias. The sample was drawn from entire sub­ populations, or randomly from the original database. The original target sample, and the responding sample, all matched the proportions found in the original database (66% women, 33% men), however this sample is biased, as both men and women are affected by colon cancer, so the clinic should see both men and women equally. The reasons why men are less likely than their female relatives to be registered is open to speculation, but this same reason may also have reduced the chance of observing any gender difference in intent to have a genetic test. Those men who chose not to attend the clinic and seek colonoscopic screening may also not intend to have a genetic test for the same reasons.

Chapter 4:Psychosocial Aspects of Genetic Testing For Colon Cancer Asynptomatic Individuals with a Family History Issues of gender and further comparisons by gender will be discussed in more detail in Chapter 6.

4.6.2 Psychological variables

Most psychological variables were related to intent to have a genetic test for colon cancer. These will be discussed in the order in which they were entered into the initial regression analyses.

Amongst the psychological variables, those comprising the theory of reasoned action (TRA) were entered first, followed by perceived behavioural control to test the theory of planned behaviour. The attitudes component of the TRA was very highly associated with intention, and accounted for the majority of the variance explained in the regression analyses. The attitudes component was the best single correlate of intention in the study. People who hold more positive attitudes are more likely to intend to have a genetic test.

Subjective normative beliefs were also highly positively associated with intent to have a genetic test in all the analyses, although attitudes explained more variance in the regression analyses than normative belief measures. The finding that family support is associated with higher intent has also been found by Glanz et al (1999).

Support has been found in this study for the power of the theory of reasoned action in explaining variance in intention. The multiple correlation of intention with attitudes and subjective norms is lower than some studies have found, and below the average level found from reviews of multiple studies (e.g. Sheppard et al 1988). The amount of variance obtained (51%) however indicates that the theory can be used to explain over half the variance in intention to have a genetic test for colon cancer. This does not mean that these factors ‘cause’ changes in intention. To demonstrate causality a longitudinal study is required. In the next study the findings of a one-year follow-up will be discussed in which the causal relationships within the theory of reasoned action will be explored.

The addition of perceived behavioural control to these variables to form the theory of planned behaviour explained no additional variance. There was a small but significant difference in perceived behavioural control across intention groups, however this was

Chapter 4:Psychosocial Aspects of Genetic Testing For Colon Cancer Asynptomatic Individuals with a Family History not linear - people holding high levels of intent reported the greatest control; people holding moderate levels of intention reported the least control. The ‘U-shaped’ nature of this relationship may indicate that people who are more cautious in their desire to have a genetic test hold this view because they are not sure whether they can or not. People holding more positive or more negative intentions to have a genetic test perceive more control. In this sample therefore perceived behavioural control may support attitudes and subjective norm, but not have such a large independent effect. The effect of perceived control may not always be in favour of acting, but may, as in this case, be a perception of power over the decision leading to a more extreme level of intention, whether positive or negative.

Anticipated affect was measured to determine whether this added to the explanatory power of the theory of planned behaviour/ reasoned action in relation to intention to have a genetic test for susceptibility to colon cancer. In analyses of variance there were differences in the directions anticipated, with those intending to have a genetic test anticipating more negative affect if they did not have the test, less negative affect if it was positive and more positive affect if they were found not to be gene carriers. Overall the levels of anticipated affect, both positive and negative were moderate in all the scenarios, indicating that not most individuals do not anticipate strong emotional reactions to genetic testing.

In the final regression analyses none of the measured anticipated affects in relation to different possible scenarios were significant correlates of intention. In the ordinal regression however, when the block containing the anticipated affect variables was entered after the theory of planned behaviour, it added significantly to the amount of variance explained in intention to have a test. In the linear regression a trend in this direction was observed. This indicates that there is a difference in anticipated affect with different intentions, but the individual measures of anticipated affect are not as strongly predictive as the components of the theory of reasoned action (attitudes and subjective norm) in explaining the variance in intent.

The other major model examined in this study was the health belief model. Four aspects of this model were tested - perceived benefits, perceived barriers, perceived susceptibility and perceived severity. All of these, with the exception of perceived severity, varied linearly with intention, which was associated with higher perceived

Chapter 4:Psychosocial Aspects of Genetic Testing For Colon Cancer Asymptomatic Individuals with a Family History benefits, lower perceived barriers and higher perceived susceptibility. The lack of a linear relationship between intent and perceived severity may be due to a threshold effect, with all individuals perceiving colon cancer as severe enough to want to reduce the risk, so there is no additional influence of increased perceived severity on intent. The measure of severity used had low internal validity, so this may have been poorly measured, or a more heterogeneous variable may have been measured than was intended. Thus is may be that a more narrowly defined measure of severity could have varied with intent in a linear way.

In the examination of the correlates of intention the health belief model was found to add significantly to the amount of variance in intention explained, after the theory of planned behaviour and anticipated affect were entered. In the final model perceived benefits and perceived barriers were still significantly associated with intention, with the strongest association being between perceived barriers and intention. To examine which theory alone explains the most variance in intention, a regression analysis was re-run, adding the health belief model first, followed by the other blocks. This analysis revealed that the initial variance in intention explained by the health belief model is less than that explained by the theory of planned behaviour. These analyses have demonstrated that although the theory of planned behaviour explains more variance than the health belief model, the health belief model does add significant explanatory power to the developing model.

It is important to note that the two components that were found to add to the model are perceived benefits and perceived barriers. Of the four components of the health belief model measured, these are the factors that, in theory have the most in common with the theory of planned behaviour so may be expected to add the least to the model. The lack of correlation between perceived severity and intention has already been discussed. Perceived susceptibility did vary by intent, however it did not add to the model to explain intent, after the variance explained by other models had been accounted for. The lack of evidence for the role of perceived susceptibility in ‘predicting’ intent is surprising as many other studies have found an association between perceived risk or susceptibility and intent to have a genetic test (Glanz et al 1999, Graham et al 1998, Struewing et al 1995b, Durfy et al 1999). The lack of association in the regression analyses may be due to the relatively homogeneous sample in this study. Although there

Chapter 4:Psychosocial Aspects of Genetic Testing For Colon Cancer Asynqjtomatic Individuals with a Family History were variations in clinical risk, most people would have been at relatively high risk of developing colon cancer compared with the general population. This may mean that perceived susceptibility in a high risk population has less importance than it might have in a comprehensive sample from the general population. There was no evidence to suggest that the theory of planned behaviour would be improved by adding a measure of perceived susceptibility, despite the original model not including this concept.

Attitude towards medical uncertainty was found to be a very strong correlate of intention to have a genetic test, with a similar degree of association with intent as subjective norms. When added after the theoretical models, attitude towards uncertainty explained additional variance in intention. Greater dislike of medical uncertainty was associated with higher intention to have a genetic test for colon cancer. This finding lends support to the hypothesis that people intend to have a genetic test to reduce feelings of uncertainty.

Contrary to most studies, there was no significant difference between people on the measure of cancer worry by intent response. Most other researchers have found that cancer worry and cancer concern have been significant correlates of intent to have a genetic test, with worry increasing with intent (Vernon et al 1999; Glanz et al 1999; Petersen et al 1999). One other study has also found no relationship between intention and cancer worry (Meiser et al 2000). It has been suggested that a curvilinear relationship may fit the data better, with people who are low and high in cancer worry being less likely to intend to have a test than those with moderate levels of cancer worry (Valdimarsdottir et al 1999). There was no evidence to suggest that this was the explanation either (the means suggest a non-significant positive linear relationship between cancer worry and intent).

This anomaly may be due to the differences between this cohort and others that have been looked at in the past. This group has lived with the prospect that they may develop cancer at some point for a number of years, and are already enrolled in a programme that will minimise the chances of them developing cancer. Many other research programmes have contacted people through a relative who is currently affected, so the concept of cancer is very salient in their minds, this may have influenced their responses. The mean response in this group is between not worrying about cancer at all or rarely worrying

Chapter 4;Psychosocial Aspects of Genetic Testing For Colon Cancer Asynq)tomatic Individuals with a Family History about it. This indicates that the overall level of worry in this group is very low, and is likely to be lower than that found in other studies.

It would be interesting to explore this topic further to determine whether there is a relationship between proximity to the illness of a relative and cancer worry, this was not measured in this study. The only index that was available in this study was the order in which families had been entered into the programme, but there was no relationship between this and cancer worry.

One issue that is particularly pertinent to this cohort is the relative reassurance of traditional screening compared with the anticipated reassurance of genetic testing. This was assessed using two questions to determine whether a clear genetic test result would be more reassuring than a clear faecal occult blood testing, or colonoscopy result. The mean response was that genetic testing would be moderately more reassuring than traditional screening methods. There was however, a linear relationship so that people with lower levels of intent held less positive views of genetic testing, and in both the lowest intent group, and the ‘yes probably’ group colonoscopies were rated as marginally more reassuring than a genetic test. This effect was not significant when entered into either a linear or ordinal regression analysis after the other theoretical constructs had been entered.

The receipt of a ‘clear’ low risk genetic test would mean that the recipient was no longer considered to be at greater than population risk, and therefore would only receive the screening appropriate to that risk level. Within the UK there is currently no national screening programme for colon cancer so screening would be withdrawn. In practice this would be assessed by clinical judgement in addition to the genetic test result, such that a person in whom polyps have previously been detected would receive follow-up assessments appropriate to that clinical condition even if the genetic test was negative. The comparative reassurance of genetic testing is therefore important, as a person who is more reassured by a colonoscopy may be reluctant to relinquish that screening, even when the evidence indicates that they are at low risk.

A reluctance to relinquish screening was found in this study when people were asked about their intended actions following receipt of a genetic test result. As expected, most people would want to continue or increase their rates of screening if the test proved to

Chapter 4:Psychosocial Aspects of Genetic Testing For Colon Cancer Asymptomatic Individuals with a Family History be positive, however few people said that they would want to stop having screening if a result was negative.

This response to the prospect of the loss of colonoscopy screening has been documented elsewhere (Michie et al 1996), and may have an impact on the uptake rates of testing for colorectal cancer in those already receiving clinical screening. Future operationalisations of the theory of planned behaviour should compare individual’s attitudes to these competing behaviours - genetic testing versus unconditional continuation of colonoscopy screening to determine the relative strength of the competing behaviours (Norman & Conner 1995).

One aspect of the reluctance to relinquish screening may be the lack of understanding of genetic testing, and its implications. People may not have fully understood that genetic testing is an alternative to colonoscopy screening, indicating definite risk levels, and mitigating all genetically linked family history. This cautious approach may be in part justified as although they may not share the same genes as an affected individual, the environment is often shared. This may indicate an increased risk factor, as the genes indicating risk of colon cancer are not 100% penetrant so even in gene carriers, environmental influences affect the development of cancer. In addition a person found not to carry a predisposing gene still has a risk of colon cancer equivalent to that in the general population (approximately 1 in 20). This risk may indeed be a justification for not wishing to relinquish screening.

The implications of genetic testing extend beyond the influence on screening behaviour to include the impact on other aspects of lifestyle, and future plans. For most people the receipt of a genetic test would lead to the adoption of a healthier lifestyle, only moderated in degree not direction of effect between different test outcomes. This is an encouraging finding, as colon cancer is not the only health risk that these participants are exposed to, so low risk test results will not lead to a decrease in healthy behaviours if their anticipated reactions are accurate predictions. This may not translate into a large actual positive effect of test result on behaviour, as intentions often do not translate into