# statistical error on a fraction

##### New Member
Hello,

I want to compute the statistical error on R, ΔR, which is a fraction N1/N2. N1 and N2 are the sizes of two samples. The Poisson error on each would be sqrt(N) but I am unsure how to compute the uncertainty on R.
Some internet search suggests that ΔR/R = ΔN1/N1 + ΔN2/N2. I have also found the same but in quadratic form: (ΔR/R)^2 = (ΔN1/N1)^2 + (ΔN2/N2)^2

Which one is correct (if any)?

Thanks!

Last edited: