have been considered in the context of angular correlation methods [@Kirian2012].

A method of measuring damage experimentally
===========================================

The statistical analysis of diffraction contrast can be used to measure the amount of damage in single molecule experiments. The average change to the atomic structure factors, characterized by $A(q)$, can be readily measured by summing diffraction patterns. This provides some information about ionization levels but not ion motion. There is more information to be gained by analyzing the fluctuations of the diffraction signal. It is not convenient to measure $SNR_{D+N}(q)$, because $B(q)$ cannot be measured directly without resolving the issue of unknown orientations and assembling a 3D dataset, effectively accomplishing a full imaging experiment. An experimentally simpler proposition, which is independent of the imaging experiment, is to measure the standard deviation of the signal within each resolution ring, averaged over all of the measured diffraction patterns. The standard deviation is proportional to $\langle B_{ij}^2(q) \rangle$ and is a measure of the speckle contrast. It will contain both contributions from the average structure of the sample and the damage noise. Unfortunately it is not clear how to separate those two contributions experimentally. Nevertheless, the standard deviation is a sensitive measure of any 