Homebrew Shop Need Index = (21 and up population/number of homebrew shops *50) + (per capita consumption in beer in gallons * 15) + (Average Internet Search Interest *35) / the highest figure (to get an index of 1.0 and lower)

Average Search Interest is calculated by Google Trend data as an average state ranking for the following homebrew related terms (Northern Brewer, Midwest Supplies, How to Brew, Home Brew Beer, Brew Beer). Northern Brewer and Midwest Supplies are selected as terms because they ranked the highest for online homebrew shop web traffic (assumption that those without access to a homebrew shop are buying online).

Per capita consumption and population numbers are from 2012 (the latest data I have).