Diffusion coefficient
The Diffusion model we are using implies that the Mean Squared Displacement (MSD) of mosquitoes, estimated as the average squared distance from the release point of all individuals at a certain time t
evolves linearly in time as
MSD(t) = 4 D t,
where D
is the diffusion coefficient.
The calculations in MRR_template.xls
aggregate captures from all surveys to compute MSD, regardless of the age (time since release), and then considers the maximum observed age for each population.
I think this is inappropriate, since MSD is a function of time. Thus, measuring the dispersion of individuals at the last date is not the same as pooling together daily measures of dispersion.
Instead, we should group captures by age and estimate MSD as a function of time, deriving the diffusion coefficient D
as the slope of the regression line with intercept fixed at 0.
In addition, captures could be adjusted by trap distribution as for MDT in order to account for lack of homogeneity.