Editing Generalized linear model (section)

==== Variance function ====
The [[variance function]] for "{{visible anchor|quasibinomial}}" data is:

:<math>\operatorname{Var}(Y_i)= \tau\mu_i (1-\mu_i)\,\!</math>

where the dispersion parameter ''&tau;'' is exactly 1 for the binomial distribution. Indeed, the standard binomial likelihood omits ''&tau;''.  When it is present, the model is called "quasibinomial", and the modified likelihood is called a [[quasi-likelihood]], since it is not generally the likelihood corresponding to any real family of probability distributions.  If ''&tau;'' exceeds 1, the model is said to exhibit [[overdispersion]].