7.5 CE rollback optimal parameters

As described in the section Performing Cost-Effectiveness Analysis (CEA), the standard method of performing a baseline CEA in the TreeAge is using the Analysis > Cost-Effectiveness or Analysis > Rankings commands at a decision node. In some cases, however, it may be useful to also display the calculated CEA values in the rolled back tree.

In order to roll back a CE tree, TreeAge Pro must be able to automatically select an optimal path at decision nodes. During CE roll back (and any analysis of a CE tree with decision nodes) TreeAge Pro uses a number of special preferences that enable the model builder to customize the roll back algorithm.

To set the optimal path parameters for cost-effectiveness calculations:

  • Choose Tree > Tree Preferences from the menu or use the icon in the toolbar to open the Tree Preferences Dialog.

  • Navigate to the category Calculation > Calculation Method > Cost-Effectiveness > Cost-Eff Params (WTP).

  • Enter values for willingness-to-pay. This can be a numeric value, such as 50,000, or a variable defined in the model.

  • (Optional) Enter values for minimum effectiveness and maximum cost, if required. (This will only show outcomes which are within these bounds).

    • The figure below shows minimum effectiveness set as 6, and maximum cost as 20000.

  • Click OK to save the Tree Preferences.

Note that you can use a variable for the "Willingness to pay" value; however, you cannot run sensitivity analysis on that variable because WTP is applied after the model is calculated, not during the model calculation.

While it is possible to set the CE parameters so that TreeAge Pro makes decisions simply by minimizing the CE ratio, it is also possible to have TreeAge Pro do the following:

  • eliminate options below a minimum effectiveness

  • eliminate options above a certain cost

  • select the most effective option within an incremental cost-effectiveness threshold.

It is also possible to invert the effectiveness measure using the Tree Preferences, as described in Inverting Effectiveness calculations.

The CE optimal path algorithm

In essence, the optimal alternative will be the most effective option with an ICER lesser than the specified willingness-to-pay (WTP). Any analysis that must select an optimal path, from the strategies at a decision node in a CE tree, does so by using the following algorithm:

  1. If minimum effectiveness or maximum cost constraints are specified, any option that fails either test is eliminated.

  2. The remaining options are ordered by increasing cost.

  3. Any option which is dominated by another less costly, more effective option is eliminated.

  4. Each option whose ICER calculated is relative to the next least costly option is greater than your WTP criterion is eliminated.

  5. The most effective remaining alternative is selected as optimal.

  6. If all options fail these tests, then the least costly option will be selected as optimal.

If a WTP of 0 is specified, as is the default, ICERs are ignored, and the least costly option will be selected. If a negative WTP is specified, TreeAge again ignores ICERs, but instead picks the option with the lowest C/E ratio.