The Dutch public are positive about the colorectal cancer-screening programme, but is this a well-informed opinion?

Colorectal cancer (CRC) is one of the most common causes of cancer death in developed countries [1, 2]. Population-based CRC screening can reduce the incidence and mortality of CRC [3‐6], which is why it is widely recommended [7‐10]. CRC screening involves potential benefits, but it also involves potential harms and risks (such as overdiagnosis, overtreatment, false negatives, false positives and risks associated with colonoscopy) [9‐14].Whether for an individual the potential benefits weigh up against the potential harms and risks is a complex issue, involving information as well as personal values [15‐17], which has been the topic of an ongoing debate among experts [13, 14, 17‐19]. Therefore, it is seen as important that people are enabled to make a well-informed and personal decision concerning participation based on a good understanding of the potential benefits and harms of CRC screening as well as their personal preferences [15‐17, 19, 20].

In general, people seem to be quite positive about CRC screening. Since the introduction of the CRC screening programme in the Netherlands in January 2014, which is provided by the Dutch government, relatively many people from the eligible screening population (adults aged 55–75) have participated (71%) [21]. In addition, the participation rates for the other cancer-screening programmes in the Netherlands (i.e. breast cancer screening and cervical cancer screening) have also been relatively high over the years (79% [22] and 64% [23], respectively), suggesting a positive view towards all forms of cancer screening. Several international studies into CRC screening suggest a generally positive view towards CRC screening as well [24‐30]. It seems that most people believe that preventive screening for colorectal cancer is a good idea [24, 25, 28‐30], important to do [27, 28] and saves lives [29, 30]. The majority of these studies, though, only studied the eligible screening population within the direct context of individual participation. They did not examine how the general public (which includes people inside as well as outside the eligible screening population) viewed CRC screening, with the exception of McCaffery et al. [26] and Bruel et al. [31]. Bruel et al. [31], however, did not examine how people view CRC screening in its entirety; they only assessed what percentage of overdetection (i.e. overdiagnosis and overtreatment) people found acceptable. Thus, although there seems to be a generally positive view towards CRC screening, it is not well known how people outside the eligible screening population, and irrespective of their own participation, view CRC screening.

There are two main reasons why the opinion of the general public towards CRC screening is of relevance. Firstly, public opinion (in addition to other factors) may – consciously or unconsciously – affect people’s personal views and attitude towards CRC screening and, consequently, their personal decision concerning participation [32‐35]. Secondly, a considerable amount of Dutch government money is spent on the CRC screening programme. Thus, it seems important to gain more insight into whether the public are supportive of how this money is spent.

Public opinion is generally defined as the opinion of the majority or the dominant opinion within the public on a publicly relevant topic [29, 30, 33, 36‐38]. Previous research into public opinion (mostly in the field of sociology or political science) generally assessed public opinion by determining the level of support [37, 39‐41] and or attitude towards a certain issue or action [29, 30, 36, 37, 40, 41] among a large group of individuals representative for the public. Studies that assessed both level of support and attitude did this mostly based on the belief that people’s attitude towards a certain issue affects their level of support. When assessing people’s attitude, some studies made a distinction between people’s personal attitude and their collective attitude [33, 36]. Someone’s personal attitude reflects how they view and evaluate a certain issue or action while considering its implications for themselves (e.g. if they think that participating in CRC screening is a good idea for themselves or not). Someone’s collective attitude, however, reflects how they view and evaluate a certain issue or action while considering its implications for the population or society as a whole (e.g. if they think that CRC screening is a good idea for the Dutch population as a whole or not).

Previous research into cancer screening and public opinion showed that people’s attitude and level of support are often associated with several factors. Examining these factors and associations will provide a broader context for interpreting people’s opinion about CRC screening. The most common key factors seem to be people’s awareness, knowledge and perceived social norm regarding a certain issue. People’s views towards a certain issue are likely to be affected by how aware and knowledgeable they are of the issue [26, 40‐43], and by how they perceive others like them to think and act regarding that issue (i.e. perceived social norm) [32, 39, 42, 44‐46]. Furthermore, the gender, age and education of the eligible screening population are often found to be associated with differences in people’s individual attitudes towards, and knowledge of, CRC screening [26, 28, 42, 47, 48]. It seems likely then that these characteristics might also be associated with differences in public opinion and knowledge concerning the CRC screening programme.

Our study aims to examine the opinion of the Dutch general public (adults 18 and older) regarding the CRC screening programme. Specifically, we aim to answer the following research questions:

In our study, we found that the Dutch public are in general positive about and supportive of the CRC screening programme. People do not seem to differ in their evaluation of the personal and societal implications of the CRC screening programme, and perceive others to be positive about the programme as well. The majority of the Dutch public (80%) was aware of the CRC screening programme, but most reported knowing more about the benefits of CRC screening than about its possible harms and risks. Level of support, attitude and perceived social norm were positively associated with each other.

Our findings seem to be in line with previous research into CRC screening, which also found people to be generally positive about CRC screening. However, previous studies mainly examined individual attitudes of the eligible screening population [24, 29, 30]. Our results indicate that the positive view towards CRC screening is not limited to those eligible for screening.

Although the majority of the Dutch public is supportive of the CRC screening programme, we did find substantial variations between the three formats used to assess support. We found the biggest proportion of support (86%) when asked directly and the smallest proportion when using the ranking question (48%). Apparently, people value the CRC screening programme less when explicitly being asked to consider that there are limited possibilities and resources and to compare the importance of the CRC screening programme to other options concerning dealing with CRC. Thus, people might believe the CRC screening programme to be a good idea in itself, but when having to choose between other options to deal with CRC, the CRC screening programme is not necessarily the option everyone would choose [55, 56].

The overall positive view of the Dutch public towards the CRC screening programme might in part be explained by the finding that people were more aware of and knowledgeable about the benefits of CRC screening than about its possible harms and risks. Previous research into CRC screening also shows that people are generally more aware of the benefits of CRC screening than of the harms and risks [28‐31, 42]. This is not surprising because, until recently, the communication about cancer screening focused on screening being beneficial and a good thing to do [11‐13, 57, 58]. Nowadays, fostering making informed decisions [19], the potential benefits as well as the harms and risks of CRC screening are mentioned in the public communication by the Dutch government [59]. However, we found that for the general public the main source of information is not the communication by the government, but traditional media. They may filter or frame their message in a certain way [60, 61], affecting what information people receive and remember best [34, 60, 61].

That most people are less aware of the harms and risks of CRC screening raises the question of whether they would still be as supportive if they knew more about the potential negative sides of CRC screening. Correlations based on our complete sample do not conclusively indicate that people are less supportive of CRC screening when more aware of its negative sides. However, among higher educated people, we found more awareness of the harms and risks and more knowledge about CRC screening in general, and they were also less supportive and positive about the CRC screening programme. Earlier research into the relationship between knowledge (on both benefits and harms) and attitude regarding CRC screening shows mixed results [26, 28, 42]. Drawing definitive conclusions concerning the relationship between knowledge and attitude is complicated by the fact that there does not seem to be an agreement on what people ought to know about CRC screening and when people have good or sufficient knowledge. Studies use different knowledge questions [26, 28, 42, 48, 62], different outcome measures [26, 48, 62] and different cut-off points [48, 62]. People in our study answered about half to two-thirds of our specific multiple-choice knowledge questions correctly. Additionally, they rated themselves as knowing not little, but also not much about CRC screening. Without a clear definition on what is seen as sufficient knowledge, it is difficult to say whether participants in our study had sufficient knowledge about CRC screening to base their views and opinion on.

Besides having knowledge about all aspects of CRC screening, it is also important that people fully understand this information and are able to use it in forming an opinion or making a decision. These ‘health literacy’ skills are often found to be associated with cancer screening participation [63, 64]. Higher educated people might be better able to handle the complex information associated with CRC cancer screening [12, 19, 65, 66]. Previous research into risk information and risk communication shows that most people find it difficult to interpret and understand information about risks, probabilities and weighing up pros and cons, especially when it is presented numerically [28, 67, 68]. In our study, we also found that people had the most difficulty when answering the knowledge questions that asked about numerical information concerning CRC screening and not with the more conceptual questions. Thus, although people are supportive of the CRC screening programme, this may not be based on a full comprehension of what CRC screening entails.

A limitation of our study is that our specific multiple-choice knowledge questions asked about the main general aspects of CRC screening. We did not include a broad range of questions about the specific benefits and the specific harms and risks. Therefore, we could not examine whether having more ‘objective’ knowledge (compared to the more ‘subjective’ self-rated knowledge we did assess) on the benefits or on the harms and risks might have been related to having a more or less positive view towards CRC screening. Another limitation might be that we used a random sample of members of a national internet panel as participants. People who participate in online research may differ in significant ways from people who do not participate in online research. They might be, for example, more interested in or positive towards CRC screening to begin with, possibly resulting in an overestimation of public support for the CRC screening programme. Thirdly, we examined whether there were any differences in public opinion related to gender, age and education. However, other sociodemographic characteristics may also be associated with differences in public opinion. For example, among the eligible CRC screening population, people with a lower income, lower social-economic status or belonging to a minority group are regularly found to think less positive about CRC screening [42, 47]. Future research could focus on examining how sociodemographic characteristics other than gender, age and education might be associated with differences in public opinion. A strength of our study is that we used three different question formats to assess level of support, providing a more comprehensive portrayal of support.

The Dutch public are supportive of the CRC screening programme, although not everyone might be as supportive when having to choose between other options concerning dealing with CRC. People’s support for the CRC screening programme may not be based on sufficient knowledge or a full comprehension of what screening entails. Future research could focus on examining what kind and amount of knowledge people need to have in order to form a well-founded opinion, and how to ensure that people are adequately informed.