# Usage of PCA - how to scale observations? [duplicate]

I want to use PCA in this kind of situation. I have three variables:

1. how many times something happened for user - positive integer;
2. total "power" of all happened events for user - real number, can be negative
3. percent of "successful hits" - real positive number 0 < x < 1

Wikipedia states that "PCA is sensitive to the scaling of the variables."

A problem is that "power" can be measured using various units. And choice of units will affect the results. I do not see a natural choice of units for the moment.

Are there any suggestions on how to scale observations for PCA?

• @AlexanderChervov I meant it as: $$x -> (x-mean(x))/(max(x)-min(x))$$, so that the variable now lies in the interval $$[-1,1]$$ – jpmuc Mar 1 '13 at 16:03