*systematic component variation SCV*. I understand the derivation with exception of the first step. Here are the

**premisses**:

\(O_i\): observed cases in region i

\(E_i\): expected cases in region i

\(\lambda_i\):

*multiplicative factor associated with region i*(I suppose it means \(O_i=\lambda_i*E_i\))

Now the following

**assumptions**have been done:

\(O_i\) is approximately Poisson distributed with mean \(\lambda_iE_i\)

\(\lambda_i\) is considered as a random variable with expected value \(1\) and variance \(\sigma^2\).

From these the following

**formula**is concluded:

var(\(O_i\)) = \(E_i^2\sigma^2\) + \(E_i\)

It tried to find out how to get the formula by the given premisses and assumptions and didn't succeed. Any idea? Thanks for help.