Participation in a Sigmoidoscopic Colorectal Cancer Screening Program: A Pilot Study¹

CRC³is a major cause of death from cancer in the developed world. The lifetime risk of dying from CRC is approximately 2.6%(1). In the Netherlands, more than 3100 patients die of CRC each year (2). Although several possible extrinsic and intrinsic risk factors for CRC have been identified (3),its exact etiology remains unknown (4). Because of limited insight into aspects of behavior associated with developing CRC,primary prevention has proved to be difficult (5, 6). However, early detection does provide an important tool for implementing secondary prevention (7, 8). Scientific evidence is accumulating to support the effectiveness of population-based screening with fecal occult blood tests and sigmoidoscopy in reducing mortality from CRC (1, 9, 10, 11, 12, 13, 14, 15, 16). Currently, there is an increasing need to evaluate whether screening for CRC on a large scale is advisable. At present, little is known about the determinants or associations of CRC screening behaviors (1, 17, 18, 19), and very little theory-based research has been done to assess determinants of participation in a sigmoidoscopic CRC screening program. This study attempts to provide some insights into the motivations that people have for their decision to participate or for their decision to refuse participation. The study was executed at the General District and University Hospital of Maastricht(Maastricht, the Netherlands) and focused on sigmoidoscopy as the method of screening for colorectal neoplasia.

Two hundred individuals were asked to take part in the pilot study. These subjects were between 50 and 60 years of age and were visiting internal medicine outpatient clinics for nephrology or general internal medicine at the General District and University Hospital of Maastricht. Exclusion criteria, which were assessed by an internist using the patient’s file and a telephone call, were: (a)known malignancy at the time of invitation; (b) an estimated life expectancy of less than 5 years; (c) having had colonoscopy, sigmoidoscopy, or barium enema in the last 10 years;(d) abdominal complaints or blood in the feces;(e) high risk for sigmoidoscopy (such as obligatory use of anticoagulant drugs); (f) hemostasis defects; (g)need for antibiotic prophylaxis for endoscopic treatment;(h) chronic heart failure (defined as inability to walk up two flights of stairs); and (i) being on hemodialysis.

Every patient visiting the internal medicine outpatient clinics for nephrology or general internal medicine who met the inclusion criteria was invited to participate. A mailed invitation package was used, which contained an introductory letter that explained the procedures of the study, a booklet with general information on endoscopic screening for colorectal neoplasia, and an answering card. The card presented the invited individuals with three options: (a) participating in the sigmoidoscopy and completing a questionnaire; (b) not participating in the sigmoidoscopy but completing a questionnaire; or(c) not participating in the pilot study at all. If subjects indicated that they wanted to participate in the sigmoidoscopy, they were phoned by an internist to assess the inclusion criteria that could not be extracted from the patient’s file.

In the screening group, participants received flexible sigmoidoscopy. Actual participation was confirmed by appointment review. Determinants of participation were assessed within 1–2 weeks before the sigmoidoscopy. Individuals who had indicated that they did not wish to participate in the sigmoidoscopy but were willing to fill in a questionnaire were mailed a questionnaire that was identical to that presented to the screening group. Data were collected between June 1997 and November 1997.

A questionnaire developed by Boer (20) assessing the psychosocial determinants of participation in a breast cancer screening program was adapted for CRC. The questionnaire included 39 questions(see “Appendix”).

Based on the theory of triadic influence (21), we distinguished three levels of influence on participation behavior:(a) ultimate factors (factors in one’s background and environment); (b) distal factors (general sense of self and social competence); and (c) proximal factors (health beliefs, social perceptions, and self-efficacy). Gender, age, having a partner, and educational level were the ultimate causes assessed in the present study. Distal causes assessed in the study were general self-efficacy and fear of CRC. Proximal causes of screening behavior were perceived severity of CRC, perceived susceptibility to CRC,response efficacy, self-efficacy, and social support. The operationalization of the concept of self-efficacy paralleled that of a validated instrument by Vernon et al. (22). This was supplemented by potential salient barriers that could increase the magnitude of the self-efficacy expectations (23). Social influence was operationalized as social support.

The scores on the items within each concept were summed. Cronbach’sα of each scale was computed to test its reliability. Two types of statistical tests were then applied to the data: (a)bivariate comparisons, using z tests andχ ² tests, to test significant differences; and(b) logistic regression analyses (24) to find significant contributions of variables in the model to participation behavior. Because the research model assumes that proximal variables directly influence participation behavior, whereas ultimate and distal variables indirectly influence participation behavior, the proximal variables were entered in the equation first, followed by the distal variables and the ultimate variables.

Of the 200 individuals invited to take part in the pilot study, 90(45%) were willing to participate in the sigmoidoscopy screening. Sixteen of these were not included in the pilot study, for example,because they had undergone colorectal surgery. Thus, 74 individuals completed flexible sigmoidoscopy. Another 60 individuals refused to participate in the endoscopic screening but were willing to fill out a questionnaire. Three of them did not return the questionnaire. This means that 74 participants and 57 nonparticipants were analyzed to study the associations of participation.

A certain selection bias might have occurred with regard to the 50 respondents who refused to participate in the study. These persons were compared with those who did participate for gender, age, and health status (hypertension, n = 92; kidney disease, n = 25; other problems, n = 82). No differences were found with regard to gender and health status. The mean age of the group that refused to participate in the study (56.4 years) was slightly higher than that of the group that did participate in the study (55.4 years; P < 0.05).

The associations of participation were assessed by comparing the participants in the sigmoidoscopic CRC screening with the nonparticipants. The scales of general self-efficacy, fear of CRC,susceptibility to CRC, and self-efficacy were found to have an acceptable level of reliability. The scales of perceived severity and response efficacy were not reliable. As a result, each of these separate items was used in the analysis. Table 1 shows the results of bivariate comparisons of participants and nonparticipants.

Using a significance level of 0.05, participants differed from nonparticipants on the concepts of gender, general self-efficacy, fear of CRC, response efficacy with regard to the certainty of having or not having CRC, self-efficacy, and informational and practical social support.

Logistic regression analysis was applied to the data (Table 2). Results revealed that the contributions of the intrapersonal variables gender, general self-efficacy, and fear of CRC were neutralized when the proximal factors were included in the equation. Self-efficacy proved to be a concept that was highly associated with participation in the screening program. Response efficacy with regard to the certainty of having or not having CRC and informational and practical support also appeared to be concepts that were associated with participation. Because research variables have been measured on different, highly divergent scales, it is not possible to compare the ORs. However, large CIs for informational and practical support indicate low reliability of the ORs found regarding these two concepts.

The participation rate in this study (45%) is comparable to that in other studies on screening for CRC in a clinical setting(e.g., Refs. 12 and 25). Nevertheless, it must be assumed that the percentages in a general population will be lower because patients already under treatment for other diseases are thought to be more health conscious (25). Whereas Atkin et al. (26)advocated a national CRC screening program using sigmoidoscopy in individuals ages 55–60 years, we feel that determinants of participation and nonparticipation in endoscopic screening programs should be carefully studied and translated into health education practice to successfully implement such a program. Some indicators of salient associations of participation can be derived from the present study.

The results of the present study indicate that nonparticipants perceive great difficulties in participating. This indicates that nonparticipants do not like the idea of participating in the program because they feel nervous about it and expect it to be painful. Furthermore, nonparticipants perceive difficulties in finding the time to participate in sigmoidoscopy. Response efficacy with regard to the certainty of having or not having CRC appeared to explain some of the variance in participation behavior, whereas informational and practical support also appeared to have predictive value.

Several findings in this study are in accordance with studies on related subjects. For example, various studies have reported that variations in self-efficacy contributed most to explaining preventive health behavior (27). Nevertheless, some critical comments need to be made about the findings. The health belief variables“response efficacy” and “severity of CRC” could not be assessed on a reliable scale. As a result, the items had to be analyzed separately, which affects the validity of the results found. In addition, it should be kept in mind that this determinant study concerned participation behavior, not participation intention. Individuals (n = 9) who wanted to participate but were excluded on the basis of exclusion criteria (such as use of medication or having undergone colorectal surgery) were not asked to fill in a questionnaire. In addition, a selection bias might have been introduced in the study. The fact that the group of people who refused to participate in the study were, on average, 1 year older than the people who did participate is an indication of this potential bias. Furthermore, this study did not exclude individuals who had a family history of CRC or prior experience with CRC screening using fecal occult blood test. Having these experiences might have biased individuals favorably toward participation in sigmoidoscopic screening. Finally, the level of significance of the determinants is influenced by the relatively small number of participants in this pilot study. It is certain that differences between the two groups would be more clear cut in a larger study population.

Despite these critical comments, the present study has prepared the ground for future determinant studies of sigmoidoscopic CRC screening participation. The model used in this study proved to be useful in explaining the participation behavior. Although the operationalization of some variables should be redefined to improve reliability, further research on participation in sigmoidoscopic CRC screening could use this combined model as a theoretical starting point. In conclusion, endoscopic screening for CRC is a promising development in the field of secondary prevention of cancer, although future research remains necessary.

I think CRC is: less severe than most other diseases, as severe as most other diseases, more severe than most other diseases, or the most severe disease I know.

Despite the progression of medical science, CRC is as severe as it was in the past: completely agree, agree, neither agree nor disagree,disagree, or completely disagree.

The chance that I will ever get CRC is: very small, small,not small/not great, great, or very great.

The chance that I will get CRC in the next 2 years is: very small, small, not small/not great, great, or very great.

The chance that someone of my age will get CRC is: very small,small, not small/not great, great, or very great.

In comparison with other persons, my chance of getting CRC is: very small, small, not small/not great, great, or very great.

Going through CRC screening results in certainty of having or not having CRC: completely agree, agree, neither agree nor disagree, disagree, or completely disagree.

When the results of CRC screening show that something is wrong, the change for cure is great: completely agree, agree, neither agree nor disagree, disagree, or completely disagree.

Going through CRC screening is: very difficult for me to do, rather difficult for me to do, a little difficult for me to do, or not difficult for me to do.

Finding time to go through CRC screening is: very difficult for me to do, rather difficult for me to do, a little difficult for me to do, or not difficult for me to do.

Transportation to CRC screening is: very difficult for me to do,rather difficult for me to do, a little difficult for me to do, or not difficult for me to do.

Because I am nervous about the screening, going through CRC screening is: very difficult for me to do, rather difficult for me to do, a little difficult for me to do, or not difficult for me to do.

Because I am reluctant to participate in CRC screening, going through CRC screening is: very difficult for me to do, rather difficult for me to do, a little difficult for me to do, or not difficult for me to do.

Because I expect the CRC screening to be painful, going through CRC screening is: very difficult for me to do, rather difficult for me to do, a little difficult for me to do, or not difficult for me to do.

Did you get advice to go through CRC screening from people in your environment (yes/no)?

Did someone in your environment offer to accompany you to the CRC screening (yes/no)?

Do you think that people in your environment understand your feelings with regard to CRC screening (yes/no)?

Do you know someone who was also invited for CRC screening(yes/no)?

Imagine that you intend to watch television tonight. A program is announced that very explicitly discusses CRC. To what extent are the following reactions evoked? You get tense (you do not get tense at all, you get a little tense, you get rather tense, or you get very tense) and/or anxious (you do not get anxious at all, you get a little anxious, you get rather anxious, or you get very anxious).

While leafing through a paper or magazine, suddenly you see an article on CRC. To what extent are the following reactions evoked? You get tense (you do not get tense at all, you get a little tense, you get rather tense, or you get very tense) and/or anxious (you do not get anxious at all, you get a little anxious, you get rather anxious, or you get very anxious).

You receive an invitation to attend a CRC screening. To what extent are the following reactions evoked? You get tense (you do not get tense at all, you get a little tense, you get rather tense, or you get very tense) and/or anxious (you do not get anxious at all, you get a little anxious, you get rather anxious, or you get very anxious).

Your neighbors tell you that someone you know well is not feeling well lately. One suspects that he/she has CRC. To what extent are the following reactions evoked? You get tense (you do not get tense at all, you get a little tense, you get rather tense, or you get very tense) and/or anxious (you do not get anxious at all, you get a little anxious, you get rather anxious, or you get very anxious).

I give up on things before completing them: completely agree, agree, neither agree nor disagree, disagree, or disagree completely.

When trying to learn something new, I soon give up if I am not initially successful: completely agree, agree, neither agree nor disagree, disagree, or disagree completely.

I am a self-reliant person: completely agree, agree, neither agree nor disagree, disagree, or disagree completely.

I feel insecure about my ability to do things: completely agree,agree, neither agree nor disagree, disagree, or disagree completely.

I give up easily: completely agree, agree, neither agree nor disagree, disagree, or disagree completely.

We thank Dr. Wim Hameeteman for support of this study. In addition, we acknowledge the kind cooperation of the secretary and nursing staff of the Department of Internal Medicine of the General District and University Hospital in Maastricht, the Netherlands.