One of the most common methods is the cumulant method, from which in addition to the sum of the exponentials above, more information can be derived about the variance of the system as follows:
where  is the average decay rate and  is the second order polydispersity index (or an indication of the variance). A third-order polydispersity index may also be derived but this is necessary only if the particles of the system are highly polydisperse. The z-averaged translational diffusion coefficient  may be derived at a single angle or at a range of angles depending on the wave vector .
One must note that the cumulant method is valid for small  and sufficiently narrow . One should seldom use parameters beyond µ, because overfitting data with many parameters in a power-series expansion will render all the parameters, including  and µ, less precise.
The cumulant method is far less affected by experimental noise than the methods below.