Polymorphic information content

It is the measure of the usefulness of an STR marker and is determined by the following formula;
\(PIC_i\ =\ 1-\Sigma_1^n\ _{pi^2}\ -\ \left(\Sigma_1^n\ _{pi^2}\right)^2\ +\ \Sigma_1^n\ _{pi^4}\)
where \(n\) is the number of alleles and \(pi\) is the allele frequency of the \(i\)th allele.