Explaining Medical Model Exceptions - Computational Intelligence in Healthcare: Advanced Methodologies - page 269

If P(6) >= P(0)
then PTH(6) >= PTH(0)
else PTH(6) < (PTH(0)
So, here a complete imputation of the missing PTH value is not possible but just a
binary solution that indicates the trend, where “1” stands for an increase and “0” for a
decrease.
4.2.3 Case-Based Reasoning
In ISOR, cases are mainly used to explain further exceptional cases that do not fit the
initial model. A secondary application is the imputation of missing data. The solutions
given by the medical expert are stored in form of cases so that they can be retrieved
for solving further missing data cases. Such a case stored in the case base has the
following structure:
1. Name of the patient
2. Diagnosis
3. Therapy
4. Problem: missing value
5. Name of the parameter of the missing value
6. Measurement time point of the missing value
7. Formula of the solution (the description column of table 3)
8. Reference to the internal implementation of the formula
9. Parameters used in the formula
10. Solution: Imputed value
11. Type of solution (exact, estimated, or binary)
Since the number of stored cases is rather small (at most 150), retrieval is not crucial.
In fact, the retrieval is simply performed by keywords. The four main keywords are:
Problem code (here: “missing value”), diagnosis, therapy, and time period. As an ad-
ditional keyword the parameter where the value is missing can be used. Solutions that
are retrieved by using the additional keyword are domain dependent. They contain
medical knowledge that has been provided by the medical expert. The domain inde-
pendent solutions are retrieved by using just the four main keywords.
What happens when the retrieval provides more than one solution? Though only
very few solutions are expected to be retrieved at the same time, only one solution
should be selected. At first ISOR checks whether the required parameter values of the
retrieved solutions are available. A solution is accepted if all required values are
available. If more than one solution is accepted, the expert selects one of them. If no
solution is accepted, ISOR attempts to apply the one with the fewest required parame-
ter values.
Each sort of solution has its specific adaptation. A numerical solution is just a re-
sult of a calculation according to a formula. This kind of adaptation is performed
automatically. If all required parameter values are available, the calculation is carried
out and the query case receives its numerical solution.