Moreover, we suspect one of the strongest determinants of the distribution of firm sales across states is domicile – that is, given the growing significance of “brick and click” retailing, we suspect many retailers’ online sales are concentrated in states where customers can visit their affiliated retail stores to preview items and seek the convenience of returning or exchanging items they have purchased online. This phenomenon which would tend to work against the Fox Study’s bias of allocating more sale to high-tax states. In the end, rather than introducing spurious (or even biased) variation into our data set (as we believe the approach taken by the Fox Study does), we elected to simply apportion online sales according to overall retail sales.