  # ds_list_vmr

In probability theory and statistics, the variance-to-mean ratio (VMR), like the coefficient of variation, is a normalized measure of the dispersion of a probability distribution: it is a measure used to quantify whether a set of observed occurrences are clustered or dispersed compared to a standard statistical model.

It is defined as the ratio of the variance $$\sigma^2$$ to the mean $$\mu$$,

$$\large D = {\sigma^2 \over \mu }$$.

ds_list_vmr(list, sample)
Returns the variance-to-mean ratio of values in a list.
COPY/// @func   ds_list_vmr(list, sample)
///
/// @desc   Returns the variance-to-mean ratio of values in a list.
///         Computes for a sample or entire population (default).
///
/// @param  {list}      list        list data structure
/// @param  {bool}      sample      true for sample, false for population
///
/// @return {real}      variance-to-mean ratio
///

function ds_list_vmr(list, sample=false)
{
var n = ds_list_size(list);
if (n == 0) return undefined;

var avg = 0;
var sum = 0;

for (var i=0; i<n; i++) avg += ds_list_find_value(list, i);
avg /= n;

for (var i=0; i<n; i++) sum += sqr(ds_list_find_value(list, i) - avg);

return sum / (n - real(sample)) / avg;
}


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