A fundamental insight of economics is that people respond to incentives. One of those incentives, though certainly not the only one, is the price of a product.

The price is in turn affected by a variety of factors, including the sales tax levied by governments.

Maine has a sales tax. Its neighbor New Hampshire does not. (They have a few things such as a "meals tax" or something like that if you eat out, but there's no broad-based sales tax.)

So can you predict the effects of this disparity?

The Maine Heritage Policy Foundation sent some observers over the state line to count the number of Maine-registered cars parked outside of Home Depot, Wal-Mart, Lowes and Target stores in a few New Hampshire locations.

They found a "silent tax revolt" (PDF) going on, with taxpayers avoiding at least $21 million a year in taxes by crossing the border.

At the time of publication, lawmakers were contemplating not ways of making the state more attractive to its own residents, but ... raising the sales tax.