# Sum of percentile rank scores of two or more variables

I need to sum some variables that are on different scales to make a new one. I'm wondering If it's correct to calculate the percentile scores first, and then to sum them up.

Imagine I have to measure general beauty and I have three variables: beauty of the hair, beauty of the face and beauty of the body. You could have a beautiful face and hair, but if you have an ugly body then you won't be considered beautiful (this is why I need to consider all the variables together and not just one by one separately). Also, you'll be perceived as beautiful if you are the most beautiful person among all the acquaintances of a specific group of people. Suppose they don't know anybody else except you and the other people in the group. Accordingly, no matter if someone more beautiful than you is in another group. This is why I'd like to use percentiles, instead of raw scores.

The three variables do not correlate. What if they do? Would things be different?

• How are the variables measured? What are the scales?
– Tim
Dec 4, 2014 at 9:42
• I have three different cases: first case, all variables are continuous (on different scales); second case, they are all ordinal (on different scales); third case, one is continuous and the other two are ordinal (on different scales). Way of measuring is reliable, I'm not worried about that in this case. Dec 4, 2014 at 9:47