The documentation page has a table (the headers are "Distribution" and "Scale") which shows how the dispersion parameter in the exponential family relates to the scale parameter for various distributions. A "scale parameter" is merely the parameter in the distribution that controls the variance, such as sigma for Normal and lambda for Poisson. The density equations at the top of the page express the variance in terms of the scale parameters, not the dispersion. The "estimate of scale" in the parameter estimates table enables you to go back and forth between the two parameters. ... View more