On 10/22/11 8:34 AM, [email protected] wrote: > I'm utterly sorry to pose such a dumb question, but: > > the variance of the values 2, 4, and 6: shouldn't that be 2.67 ? The > StatUtils and DescriptveStatistics give me 4. > > My calculation (that I checked a dozen times) is: > (2-4)^2 * 1/3 + (4-4)^2 * 1/3 + (6-4)^2 * 1/3
The implementations in the classes above use the bias-corrected formula for the variance, which makes the denominator above equal to 2. If you want the non-bias-corrected version, you have to use the Variance class directly and set the biasCorrected property to false. The javadoc could be clearer here and it would probably be good to add a populationVariance method or a version of getVariance in these classes that takes a boolean to determine whether or not the result is bias-corrected. I will open a JIRA for that. Phil > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [email protected] > For additional commands, e-mail: [email protected] > > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
