[islwyn]

Hello

I would like to know how you calculate the variance of a ratio.
e.g. 3/4 , 75/100 , 60/90
What is the variance for the 3 ratios

[Unknown008]

Just simplify each of them.

3/4 cannot be simplified any longer.
75/100 can be. There are common factors in the numerator and the denominator.
60/90 can be simplified too.

Finally, you'll see which does is the one not like the others.

Post your answer, please :)

[islwyn]

Hi

I think you've missed understood my question but thanks for trying
If my numbers were
4 , 10 , 15 , 12 , 6
The variance would be 19.8

How do calculate the variance of 12/3, 100/10, 30/2, 144/12 and 600/100

Quite clearly the denominator for the final number is far greater than denominator for the other numbers which will affect the variance - do you see the dilemma ?

[Unknown008]

Ow, sorry... haven't done that yet at school. Statistics will be for next year.

I just checked wikipedia and variance is equal to the mean of the squares minus the square of the mean.

Mean of squares = 104.2
Square of mean = 88.36
Variance = 15.84

I don't understand how you got 19.8. :confused:

Well, if my interpretation is really off the true facts, just disregard my posts and wait for a someone with better knowledge than me. There are quite a few here, namely galactus, ebaines and Perito.

[ebaines]

The variance for a set of n numbers is calculated from:



where is the mean of the numbers. So given the numbers 4, 10, 15, 12, 6 the variance turns out to be 19.8, as islwyn said.

For the "ratios" you've asked about, I would assume that these are actually fractions, so you would calculate the variance for a set of 3 numbers:
3/4 = 0.75
75/100 = 0.75
60/90 = 0.667

You'll find that the variance for this set of three numbers is 0.002315