Report in English with a Dutch summary (KCE reports 45A)

144 Screening for Colorectal Cancer: Appendices KCE reports vol.45
All parameters and variables included in the model are presented in table 30.
Uncertainty is accounted for in the model by including all estimated variables
with their respective distributions. Estimates and distributions are derived from
literature or from expert opinion if no data were directly available from
literature. This approach allows probabilistic sensitivity analyses and the
construction of confidence intervals around the point estimates for total costs
and costs per CRC detected resulting from the model. Parameters for which
precise data are available, such as costs of specific procedures, are included in
the model without a distribution.
The basis for the assumed value and distribution of each variable in the model is
briefly explained in the following paragraphs.
8.1.1.1 Exclusion of individuals at high risk
Mass screening is targeted at individuals at average risk. Therefore individuals at
increased or high risk should not be included in mass screening but offered
regular health care. In both the GP and mailing system, individuals at high risk
are excluded from mass screening. In the GP system the GP performs a prescreening
risk-stratification and informs the patients about the eligibility for
mass screening. In the mailing system, the accompanying letter will clearly state
that individuals who are already being followed-up for their increased CRC risk
should not participate. In case of doubt they would be adviced to contact their
GP.
We do not have precise data on the actual number of individuals that will be
excluded for this reason. A few studies estimated the prevalence of having a
family history of CRC in at least one first degree relative at 5 to 10% (see
chapter 3.5). In the literature it is assumed that about 25 to 30% of cancers
occur in individuals at increased risk. Assuming on average a doubling of the risk
in this group, this would correspond to a proportion of 14 to 18% of the
population that should be excluded from mass screening. We therefore used a
point estimate of 16% with an uncertainty ranging from 14% to 18% in a Betadistribution.
8.1.1.2 Participation
8.1.1.3 Compliance
Participation is defined as going to the GP in the GP system or returning the
test kit to the laboratory in the mailing system. In RCTs participation to FOBT
in the first round of screening ranges from 60% to 69,5% (see table 23). The
Cochrane meta-analysis 24 reported 67%. Real world experiences in different
countries (see table 28), however, indicate more variation in participation,
ranging in Europe from 20% in the Czech Republic to 75% in Finland. In chapter
5 we showed that the median participation rate to programmatic offers of
FOBT is between 40 and 50%, and that approximately 50% can be obtained with
minimal prompting. For the budget impact model we used a point estimate of
45% with an uncertainty ranging from 15% to 75% in a Beta-distribution.
Compliance is defined as accepting colonoscopy after a positive FOBT result. In
our model, compliance with colonoscopy is assumed to be 87,5%, with
uncertainty limits ranging from 80% to 95% in a Beta-distribution. This
assumption is based on experience in other countries (see chapter 7), on
expert opinion and supported by evidence from the Burgundy and the Funen
trial that report a compliance rate with colonoscopy after a positive FOBT of
85% and 82% respectively (see table 29).