The accommodation index is a statistic used in the neurosciences for describing spike train data.
Many methods of experimental neuroscience, such as voltage clamp recordings, give their output in the form of measured voltages of individual neurons.
It is often useful to be able to describe the data in terms of the spike timings; for instance, when optimizing a compartmental model towards observed behaviour, statistics such as this can be used to gauge error.
Various statistics are used to do this, such as spike rate, average interspike interval, and the accommodation index.
It is similar to other measures of accommodation such as the local variance introduced by Shinomoto et al. in 2003.
It is defined by the average of the difference in length of two consecutive interspike intervals (ISIs) normalized by the summed duration of these two ISIs.