where index {{math|i}} is defined over the set of all non-isomorphic n-size graphs. Another statistical measurement is defined for evaluating network motifs, but it is rarely used in known algorithms. This measurement is introduced by Picard ''et al.'' in 2008 and used the Poisson distribution, rather than the Gaussian normal distribution that is implicitly being used above.<ref name="pic1">{{cite journal |vauthors=Picard F, Daudin JJ, Schbath S, Robin S |title=Assessing the Exceptionality of Network Motifs |journal=J. Comp. Bio. |year=2005 |volume=15 |issue=1 |pages=1–20|doi=10.1089/cmb.2007.0137 |pmid=18257674 |citeseerx=10.1.1.475.4300 }}</ref> | where index {{math|i}} is defined over the set of all non-isomorphic n-size graphs. Another statistical measurement is defined for evaluating network motifs, but it is rarely used in known algorithms. This measurement is introduced by Picard ''et al.'' in 2008 and used the Poisson distribution, rather than the Gaussian normal distribution that is implicitly being used above.<ref name="pic1">{{cite journal |vauthors=Picard F, Daudin JJ, Schbath S, Robin S |title=Assessing the Exceptionality of Network Motifs |journal=J. Comp. Bio. |year=2005 |volume=15 |issue=1 |pages=1–20|doi=10.1089/cmb.2007.0137 |pmid=18257674 |citeseerx=10.1.1.475.4300 }}</ref> |