F 0.5 and F2 Scores

June 12, 2016

As explained in last night's tip, an F-score is a combined measure of precision and recall.    An F1 score gives equal weight to precision and recall.   A version of the equation, which allows different weights to be assigned to precision or recall would be expressed this way:

 

Fß = (1+ß²)     Precision  * Recall 

                     (ß² Precision) + Recall

 

The beta symbol, ß ,  is used in mathematics to indicate when a variable can be entered.   The term F2 score will be used when twice the weight is given to recall as opposed to precision.   When giving twice as much weight to precision, an F 0.5 score is used.   

 

In Excel we can use these formulas to calculate these two types of equations:

 

F 0.5 score Excel =((1.25)*((A9*B9)/((0.25*A9)+B9)))

 

F2 score Excel  =((5)*((A9*B9)/((4*A9)+B9)))

 

 

. . . and a formula for the general Fß equation, allowing the user to grant varying weights to precision or recall would be:

=((1+(C9^2))*((A9*B9)/((C9^2*A9)+B9)))    

 

.  . . where column C  gives the  ß value.

 

See a demonstration of these formulas in an Excel spreadsheet on my YouTube channel:

 

 

 

 

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