In the Probability section on the left panel you can enter data values into the probability statement to determine the probability or proportion for an age in defined regions Probability P x Data value here Probability proportion for the indicated region here According to our normal model what approximate age is the boundary for the youngest 15 of Congress members Enter 0 15 into the probability field so SALT will compute the boundary age and display the age in the data value field Rounded to one decimal place approximately 15 of members of Congress are expected to be younger than X years according to our model