Rather,foraspecific segment,covarianceisanincreasing
function oftheproductoftheexpectedvalues λji; λki. Therateofincreaseisnotnecessarilyunrestricted;increasesinthe
expectednumbersofanytwocrashtypesareoffsetbythedegreeofheterogeneity(theoverdispersionparameter)present
in thedata.Inaddition,iteliminatesthestrictupperboundtothecorrelationthatwasobservedfortheothertypesof
multivariatecountmodels