Davies: Computer Vision, 5th edition: Solutions to selected problems 44
20.1
If more sources of error are applied to the same data, the variances have to be added.
Furthermore, if each source contributes equal amounts of error, the variance has to be
multiplied by the number of error sources M. In the inverse situation, if more data is
supplied and the error sources are unchanged, the variances are divided by the total
number of data points N. Thus there is a natural ratio M/N governing the overall error. In a