It's easy enough to find out how long copyrights last, but much harder to decide how long they should last—but that didn't stop Cambridge University PhD candidate Rufus Pollock from using economics formulas to answer the question. In a newly-released paper, Pollock pegs the "optimal level for copyright" at only 14 years.

Pollock's work is based on the promise that the optimal level of copyright drops as the costs of producing creative work go down. As it has grown simpler to print books, record music, and edit films using new digital tools, the production and reproduction costs for creative work in have dropped substantially, but actual copyright law has only increased.

According to Pollock's calculations (and his paper [PDF] is full of calculations), this is exactly the opposite result that one would expect from a rational copyright system. Of course, there's no guarantee that copyright law has anything to do with rationality; as Pollock puts it, "the level of protection is not usually determined by a benevolent and rational policy-maker but rather by lobbying." The predictable result has been a steady increase in the period of copyright protection during the twentieth century.

Because Pollock's "optimal level for copyright" falls over time (as production and reproduction costs fall), policy makers need to be especially careful when contemplating increased copyright terms. It's difficult to scale back rights that have once been granted, so "it is prudent for policy-makers to err on the low side rather than the high side when setting the strength of copyright."

Neither the US nor the UK are in any danger of rethinking copyright law from scratch, but if they were looking for guidance in how to set up their systems, Pollock has it. He develops a set of equations focused specifically on the length of copyright and uses as much empirical data as possible to crunch the numbers. The result? An optimal copyright term of 14 years, which is designed to encourage the best balance of incentive to create new work and social welfare that comes from having work enter the public domain (where it often inspires new creative acts).

Pollock has been an advocate for restricted copyright terms and stronger public domain for years; we earlier spotlighted a brief essay of his on the "Value of the Public Domain" that is well worth a read. His new work is getting some publicity too: it has already been highlighted by Boing Boing and will be presented at a conference in Berlin this week.