spread
may be
set to true
resulting in random variations of several parameters. Handling
spreading is illlustrated in figure 4.
When an analysis starts Loop::initialize
passes Scenario::spread
on to
the member Loop::spread
. Various components support random fluctuations of
their parameters, and if Scenario::spread
is true these random
fluctiations are applied to these components. Figure 4
illustrates where random fluctuations may be applied:
Mammo
modality's systematicError
;
Screening's attendanceRate
;
Tumor
components:
Survival
;
Growth
;
TumorInfo
:
Beir7
;
Incidence's
carrier specifications.
Random fluctuations can be applied to means, standard deviations and proportions.
For means the normal distribution is used by default. For example, the
specification of the meanAge
distribution, specifified for carrier
Normal
in the Incidence
component of the Tumor
specification may
look like this:
# value spread distr. meanAge: 72.9 .552 Normal95% of the mean-values which are randomly drawn from this distribution are located in the interval 71.8 to 74.0. When spreading is used, thus computed mean values are used as mean values of the
Normal
carrier during
the actual simulations.
For standard deviations the chi2 distribution is used, ensuring that
the standard deviation that is used for the simulations exceeds 0 (see the
next section for a description of the theory and implementation in
simrisc
). For example, the standard deviations of the Normal
carrier
distribution may look like this:
# value spread distr. stdDev: 21.1 .048 NormalThe number of degrees of freedom of the chi2 distribution to use
N - 1
, where N
is the number of cases that are used in a simulation.