4b: Decision Modes
In this chapter you will add another decision task to the process-description you created in the previous chapters. The new decision will recommend one of two treatment plans – surgery or chemotherapy – or both, based on the data collected by the Patient history enquiry
To download the process-description created in the previous chapter select File > Load Process Description From Web Repository. If you are logged in, the Load Process Description dialog appears; otherwise, you have to log in (if you don’t have a personal account, use the guest account: User Name = Guest; Password = testpass). Navigate to World\Tutorials and select and load Chapter04a_create_a_simple_decision_based_on_results_of_an_enquiry.
1. Add a Decision
Click on the Decision button in the toolbar; then click in the network view area to place the task.
Make sure the new decision is selected, and enter the following information in the Task Attributes panel:
| Instance Name: | Cancer_treatment_decision |
| Caption: | Cancer treatment |
2. Add Candidates to the Decision
This decision will have three candidates: Surgery, Chemotherapy and Other, in case surgery and chemotherapy are not recommended.
Surgery Candidate
In the Candidates tab of the Decision Specific Attributes panel, enter the following information:
| Name: | Surgery |
Click Add.
Chemotherapy Candidate
Add the second candidate. Use the following information:
| Name: | Chemotherapy |
Click Add.
Other Candidate
Add the third candidate. Use the following information:
| Name: | Other |
Don’t forget to click Add.
3. Add Arguments For Each Candidate
The Cancer treatment decision will be based on two of the data items that are entered by the clinicians in the Patient history enquiry: the patient's age and the biopsy result.
The table below displays the relationship between the data items and the possible candidates (note that the information in this table is not reliable and was fabricated for the purpose of this exercise).
| Surgery | Chemotherapy | Other | |
Biopsy |
Positive result | Positive result | |
| Age | Not recommended for older people | - | |
| Notes | Should be recommended if the other two candidates are not recommended | ||
Based on this table, arguments for each candidate can now be added.
Select the Arguments tab of the Decision Specific Attributes panel.
Surgery Candidate
From the Candidates drop-down list box, select the Surgery candidate.
From the table above it can be seen that a positive biopsy result is an argument for surgery. On the other hand, an older age is an argument against surgery. Two arguments can be constructed to ensure appropriate selection of the Surgery candidate; one for the candidate, and one against it:
1. Argument for the Surgery candidate
Enter the following information:
| Condition: | biopsy = Positive |
| Description: | Biopsy result is positive |
| Support: | + (For) |
Click Add.
2. Argument against the Surgery candidate
Enter the following information:
| Condition: | age >= 70 |
| Description: | Patient is elderly |
| Support: | - (Against) |
Click Add.
Assuming the default recommendation rule is used, if the biopsy result is positive, surgery will be recommended – unless the patient is elderly.
Chemotherapy Candidate
From the Candidates drop-down list box, select the Chemotherapy candidate.
From the table above it can be seen that a positive biopsy result is an argument for chemotherapy.
1. Argument for the Chemotherapy candidate
Enter the following information:
| Condition: | biopsy = Positive |
| Description: | Biopsy result is positive |
| Support: | + (For) |
Click Add.
Assuming the default recommendation rule is used, if the biopsy result is positive, chemotherapy would be recommended.
Other Candidate
The Other candidate will not have any arguments; instead, you will deal with this candidate by modifying its decision rule.
4. Define a Recommendation Rule For Each Candidate
Looking at the table above, which displays the relationship between the data items and the three candidates, it can be seen that if the patient’s biopsy result is positive, both surgery and chemotherapy are recommended – unless the patient is elderly, in which case only chemotherapy is recommended. The arguments you have constructed for these candidates, together with the default recommendation rules, will ensure that this will be the case.
The Other candidate, however, has no arguments; as long as the default recommendation rule is used, it will never be recommended. You will now modify the Other candidate’s recommendation rule, so that it will depend not on the candidate’s arguments, but on whether the other two candidates, Surgery and Chemotherapy, are recommended or not.
Select the Decide tab of the Decision Specific Attributes panel.
From the Candidates drop-down list box, select the Other candidate.
In the Rule field, enter the following expression:
| Rule: | netsupport(Cancer_treatment_decision, Surgery) < 1 AND netsupport(Cancer_treatment_decision, Chemotherapy) < 1 |
5. Multiple Selection of Candidates
By default, only one candidate can be selected for a given decision. This is satisfactory when the candidates of a decision are mutually exclusive, as in the Diagnosis decision. But in the Cancer treatment decision there are situations in which both surgery and chemotherapy should be carried out. When more than one candidate can legitimately be selected, the selection mode of the decision task has to be modified.
To allow the selection of more than one candidate, select the Cancer treatment decision.
In the Properties tab of the Decision Specific Attributes panel, select Multiple Selection.
Note: The Tallis Tester will allow you to select more than one candidate even if Single Selection is selected. The Multiple Selection attribute will only have an effect when the process-description runs in a web-browser.
6. Create a Scheduling Constraint
Create a scheduling constraint between the Diagnosis decision and the Cancer treatment decision, so that the Cancer treatment decision will run after the Diagnosis decision is completed (for more information about creating scheduling constraints, see Step 5 of Chapter 1).
7. Save the Process-Description
For more information about saving see Step 6 of Chapter 1.
8. Run the Process-Description in the Tallis Tester
For more information about running see Step 7 of Chapter 1.
Run the process-description to make sure that the Cancer treatment decision functions as it should.
Note that at the moment the Cancer treatment decision runs after the Diagnosis decision even if the diagnosis isn’t cancer. We will deal with this in the next chapter.
- To test whether both the Surgery candidate and the Chemotherapy candidate get recommended, enter 55 for age and Positive for biopsy result.
- To test whether only the Chemotherapy candidate gets recommended, enter 75 for age and Positive for biopsy result.
- To test whether the Other candidate gets recommended, for biopsy result enter either Negative or No biopsy result.
Exit the Tester before going on to the next chapter.