MODELOS DE GESTIÓN DEL TALENTO HUMANO

Intent has been the main dependent variable of interest in many of the studies. In most studies this has been measured on a five point scale, however this is usually very skewed, with most people saying that they probably or definitely intend to have a genetic test. In the majority of studies the responses have been dichotomised to yes definitely compared with all other responses (Lerman, Marshall et al 1996; Petersen et al 1999; Glanz et al 1999; Lerman, Daly et al 1994; Struewing et al 1995b; Meiser,

Chapter 2 Psychological Aspects of Genetic Testing

Butow, Barratt Butow et al 2000). The responses have then been compared using logistic regressions. The small numbers of people giving responses other than yes definitely or yes probably have meant that there have been insufficient numbers to meaningfully combine the two positive responses and compare them with the negative or more neutral responses. This is a problem of insufficient power, which may have been overcome by recruiting more respondents.

One problem with dichotomising the sample at this point is that the prediction is then who is likely to definitely intend to have a genetic test, compared with predominantly those who say they probably would intend to have a genetic test. It is unclear whether this is going to be a useful distinction, as those who say that they probably intend to have a genetic test may simply be more cautious in their endorsement. ‘Probably’ is still a relatively positive quantifier - meaning that it is likely that they will have a test. Dichotomising also eliminates the possibility of revealing whether there is a linear pattern in the prediction of intent by various factors. For example is perceived risk linearly associated with intent - does high risk equate to high intent, moderate risk to moderate intent and lower risk to lower intent or is there a threshold effect with only a certain level of risk necessary to produce positive intent to have a test? By dichotomising the sample these researchers have lost some of the original sensitivity and are answering a less interesting question (are people who say ‘yes definitely’ different fi’om those who say ‘yes probably’).

In this study intent will be examined with the assumption that it represents an underlying linear variable, using both linear regression techniques and ordinal regressions. The sample is larger than most of the studies reported here so this will also increase the numbers of people who endorse responses other than ‘yes definitely’ or ‘yes probably’.

Chapter 2 Psychological Aspects of Genetic Testing

2.8

Areas Identified as Needing Research

The studies on genetic testing to date provide generally consistent results with some variations. In this thesis previous findings should be replicated, and certain areas will be examined in more detail than in previous studies.

One area that has not been explored in great detail is the transferability of models of health behaviour to the issue of genetic testing. Most of those studies that have employed a model have used the health belief model to varying degrees. Few studies have used this model in its entirety, and where it has been used it has often been used in conjunction with other factors, so the model itself has not been tested. Another model used was the transtheoretical model of change (Vemon et al 1999), for which support was found. The ‘attitudes’ component of the theory of reasoned action has also been used (Glanz et al 1999), but the whole model was not used and the sufficiency of the model was not tested; rather it was combined with other variables, so the influence of these constructs on behaviour is not clear. The use of models has been widely established in other areas of health psychology, although some problems emerge when these are applied to genetic testing. This will be discussed in greater detail in the next Chapter.

Previous studies of why people intend to have a genetic test have, with a few exceptions, used survey methods. There have been flaws in some of this work, as many researchers have collapsed intention into dichotomous variables, and so have lost some of the original sensitivity. In this study the linear nature of intent will be explored using both linear and ordinal regressions which preserve the original data.

Gender has been explored in a number of studies, but a consensus has yet to be reached on whether there are any gender differences. One problem has been that for breast / ovarian cancer, the effects of carrying a predisposing gene vary between genders, this may explain why women are more interested in testing than men. The differences in intent though could be due to differences between men and women in their evaluation of and anticipated reactions to knowing their genetic composition in general rather than because they are specifically considering their risk of breast/ ovarian cancer. The

Chapter 2 Psychological Aspects of Genetic Testing

findings in studies of intent to have a genetic test for colon cancer are more equivocal. Although women have been found to be more interested in some studies this has not been found in all reports. Differences between men and women will be examined in terms of their evaluation of and anticipated reactions to genetic testing for colon cancer.

Another area which has received little attention since the early studies of HD is the effect of genetic testing on the partners of people at high risk, and whether they actually want their partners to undergo a genetic test. This will be examined by recruiting both people at high risk of developing colon cancer and their partners to the study to compare their views of genetic testing.

Few studies have recruited both affected and unaffected individuals, and those which have, have used this factor as an additional predictor variable, rather than exploring the differences. There are likely to be a number of differences as testing in people who have had cancer is seen as confirmatory, whereas it is predictive if a person has no clinical signs of cancer. Struewing et al (1995b) found that although not significant, women who had had breast or ovarian cancer held higher intent than the men and women in the study who had not had cancer. In another study (Cappelli et al 1999), women who had breast cancer were compared with a general population control group. In this study those women who had breast cancer held higher levels of intent than women from the general population. This study does not inform the debate about whether affected women are more likely to want a test than unaffected women at high risk are, and whether there is likely to be a difference between the women on other aspects related to genetic testing. In this thesis this issue will be addressed, to determine whether genetic testing has a different meaning for those people who have already had cancer, compared with those at increased risk, but currently unaffected.

The issue of risk is one that has not been adequately explored in relation to genetic testing for colon cancer. Many studies use participants who are at only a low or moderate risk of developing colon cancer, and there have been insufficient comparisons across risk categories to determine the influence of objective risk on intention. The use of high risk samples who meet the Amsterdam Criteria, people at a

Chapter 2 Psychological Aspects of Genetic Testing

slightly lower, but still at risk and a general practice sample will permit a greater investigation of the influence of objective risk on psychological aspects of genetic testing for colon cancer.

One more area that deserves greater research is the comparability of outcomes for different disease models. With the completion of the Human Genome Project and the development of better technical skill to identify predisposing genes, it is possible that in the near future genetic testing will be available for a greater diversity of diseases. The time required to pursue an in depth evaluation of all possible genetic disorders and the possible psychological consequences will not be available. It will be necessary to determine the likely effect that testing for any given disease will have, with consideration to the penetrance of the gene, the severity of the illness and any additional disease specific factors. Determining similarities and differences across disease models will permit the development of a model of intent, which should be applicable to other diseases.

Chapter 3: Theoretical Basis of Thesis

Chapter 3