15.3 Changing what the tree calculates

Some basic tree calculation preferences were introduced in the Create and configure your model section of the Building Decision Trees section and this included:

  • the calculation method

  • the active payoff(s)

  • the optimal path criterion

  • numeric formatting

To view in detail the tree’s current calculation method, or to make changes to these settings, open the Tree Preferences dialog.

To view/edit the calculation method preferences:

  • Choose Tree > Tree Preferences from the menu.

  • Select the category Calculation > Calculation Method.

Selecting calculation method

The choice of calculation method determines the formula used to calculate values for nodes in your tree. There are three kinds of calculation methods:

  • Simple, single-attribute calculations;

  • Multiple-attribute calculations, including: Benefit-Cost and Multi-Attribute (weighted);

  • Cost-Effectiveness, which is a form of multi-attribute calculation used in Healthcare.

Simple calculations are just that — expected values are calculated for the nodes in the tree based simply on the values in the active payoff set. If, as described above, your tree included multiple attributes — such as monetary benefits in payoff #1 and costs in payoff #2 — the two sets of payoff values could be combined in a single calculation using the Benefit-Cost calculation method’s formula.

To change the calculation method:

  • Roll back must be turned off.

  • With the Preferences dialog open to the Calculation Method category, select the radio button for the appropriate calculation method.

  • If you select a calculation method for the first time in a particular tree, the settings for payoffs, optimal path criterion, and numeric format may need to be modified.

Some important things to note in relation to the calculation methods:

  • Changing calculation method (or other) preferences will not affect the content of your tree. Values or formulas already entered in payoff #1 will not be lost by switching the active payoff set from #1 to #2, for example. Only the calculation and display of values will be affected; the changes to the calculation preferences can be reversed at any time.

Additional Tree Preference categories contained within the Calculation Method group are used to specify preferences associated with each calculation method. The next sections describe the different Calculation method groups: