# Probabilistic Base Case Tornado Diagram

The Probabilistic Base Case Tornado Diagram evaluates the outcome of a model when chance events are individually set to high and low states and compares the results to the outcome of the model when all events vary across their states.

__Generating a Base Case Tornado Diagram__

- Select Home | Sensitivity | Tornado | Probabilistic Base Case. The Tornado Setup dialog will come up.
- Assign Low, Nominal and High states for the chance events in the model (see "Assigning States" below).
- Click OK.

__Assigning States__

The process for setting up a Probabilistic Base Case Tornado Diagram is identical to that of the Base Case and Initial Decision Alternative tornado diagrams. Please see Base Case and Initial Decision Alternatives Tornado Diagrams for a full description of assigning states.

__Results and Policy Changes__

To produce a Probabilistic Base Case Tornado Diagram DPL will run the model several times: it will run the full model to establish a base case policy and the expected value of the model. DPL will then run the model multiple times for each chance event, setting it once to the specified Low state and once to the specified High state, while all other events are set to their specified Nominal states. It will then display a bar for each event indicating the difference in the output value under the optimal policy as the event is varied from the Low to High state. If the policy for the Low or High state is different from the base case policy, DPL will indicate this with color. Blue means that the policy changed for the Low state of the event, magenta means the policy changed for the High state. The color change occurs halfway between the base case vertical line value and the end of the bar, and does not indicate the exact location of the policy change.

The output value of the base case, or expected value of the model, is indicated by a vertical line. In most cases, the ends of a bar will lie on either side of the base case value line. In cases where both ends lie on the same side of the line, the bar will not intersect the vertical base case value line.

__Value Nodes in Base Case Tornadoes and Initial Decision Alternatives Tornadoes__

You can add bars for value nodes to the diagram by selecting Chart | Series | Data | Modify while viewing the diagram. After you specify a Low and High value for a variable and click OK, DPL will run the analysis and insert the new bar. This bar is, like all others in this diagram, compared to the base case, where all chance events have been set to vary across their outcome states.

__Updating the Diagram__

If you change your model and wish to update the bars in the diagram, select Chart | Series | Data | Refresh. DPL will redo all the comparisons in the diagram using the current model and the previously specified low, nominal and high states for each chance event. If a chance event has changed and has a different number of states, DPL will ask you to confirm the low, nominal and high states for all the chance events in the model.

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

*See Also*