# Event Tornado Diagram

Event Tornado Diagrams are used to compare the relative effects of the uncertainties in probabilistic models. The meaning of each bar depends on the type of the event tornado (see below).

__Results and Color Changes__

DPL runs the model several times: once to establish a base model run and once for each chance event. It will then display a bar for each event indicating the variance in the model risk profile under the optimal policy.

The width of a bar indicates the difference between the 10th percentile and the 90th percentile of the model risk profile for the sensitivity run. The change in color occurs at the 50th percentile. (The bar is yellow between the 10th and the 50th percentiles; red between the 50th and 90th percentiles.) The vertical line indicates the expected value of the base model run.

For Deterministic Event Tornadoes, each bar indicates how much uncertainty there is in the range of outcomes when the sensitivity event is the only uncertainty in the model (assuming Always Gamble has not been used, see Event Tornado Overview for more information). The events closer to the top of Deterministic Event Tornado contribute more to the uncertainty of the model and probably should not be removed. Events nearer the bottom of the tornado contribute less to the uncertainty in the model and potentially could be handled deterministically.

In a Deterministic Event Tornado, there will also be a bar called +MINIMUM MODEL RANGE+, which indicates the variance in the model risk profile of the base run. The variance in the +MINIMUM MODEL RANGE+ is often zero since all lotteries are replaced with their expected values in the base run for a Deterministic Event Tornado. The variance may not be zero if the decision tree is asymmetric or if always gamble has been used. See Don't Gamble. If the +MINIMUM MODEL RANGE+ bar has no width it will not appear. If you wish to view this bar anyway, click the dialog box launcher for Chart | Series | Point, and select the +MINIMUM MODEL RANGE+ bar.

For Probabilistic Event Tornadoes, each bar indicates the reduction of uncertainty that results when the sensitivity event is replaced with its expected value (for the handling of Don't Gamble and Always Gamble, see Event Tornado Overview). The bars are sorted narrowest to widest in a Probabilistic Event Tornado. The events nearer the top of the tornado contribute more to the uncertainty of the model and probably should not be removed. Events nearer the bottom of the tornado contribute less to the uncertainty in the model and potentially could be handled deterministically.

In a Probabilistic Event Tornado, there will also be a bar called +ORIGINAL MODEL RANGE+, which indicates the variance in the model risk profile of the base run. The variance in the +ORIGINAL MODEL RANGE+ will often be the largest variance in the tornado because in the base run of a Probabilistic Event Tornado no chance events have been replaced with their expected values (unless Don't Gamble has been used).

* Versions:* DPL Professional, DPL Enterprise, DPL Portfolio

*See Also*