The linear noise approximation is a method for estimating covariances between species particle numbers.
[1] Pahle, Jürgen, Joseph D. Challenger, Pedro Mendes, and Alan J. McKane. “Biochemical Fluctuations, Optimisation and the Linear Noise Approximation.” BMC Systems Biology 6, no. 1 (July 17, 2012): 86. https://doi.org/10.1186/1752-0509-6-86.
