# Poisson distribution, Standard deviation, fitting line

Let's say I have system A, B, C, and D. Each system contains 10000 numbers generated by Poisson distribution. The difference is the mean is different for different systems. I calculated the std dev for each distribution corresponding to each system. I plot the standard deviation with respect to mean numbers. (I observe std deviation increases with mean). I want to fit the plot with some line, which gives me the general estimate of std dev with respec tt the mean number. I need help in finding the fitting line!

Thank you!

## 1 Answer

This sounds like simple linear regression. Your x-value is the vector of means and the y-value is the vector of corresponding standard deviations:

$$Y = X\beta$$

$$\beta$$ a vector containing the slope of your regression line and the offset term.

In R for example you can do fit <- lm(Y~X).