Applies to: @RISK 5.x and Up

Generating a Lognormal Distribution with Two Percentile Parameters in @RISK

Question
In @RISK, is there any way to generate a lognormal distribution using only two percentile parameters, even though the lognormal distribution normally requires a third percentile that is automatically calculated?

Answer
Yes. You can do this by using the alternate parameterization option for the lognormal distribution.

Steps

1. Open Define Distribution.

2. Go to the Alt. Parameters tab and select LognormAlt.

3. In the left-hand section of the dialog, click in the Alternate box next to Parameters.

4. Click the drop-down arrow that appears.

5. Under Parameter Selection, select the radio button next to Location.

6. Adjust the remaining two percentile values as needed.

7. Click OK.

8. Back in the Define Distribution dialog, set Loc (location) to 0.

This approach allows you to define the lognormal distribution using two percentile parameters while explicitly fixing the location parameter, avoiding the need to work with an automatically generated third percentile.