A copyright is a monopoly, granted in order to stimulate work in “science and the useful arts.” It is in the interests of users of such work that the monopoly is granted for a limited time. So what should the limit be? Rufus Pollock has researched this question, and posted his answer.
Using a simple model we characterise optimal term as a function of a few key parameters. We estimate this function using a combination of new and existing data on recordings and books and find an optimal term of around fourteen years. This is substantially shorter than any current copyright term.
Rufus is a Ph.D. student at Cambridge (the one in England, not the one across the river from Boston). His post includes an abstract, from which I quote above, and a link to the full paper. I followed links to the post from BB Cory and from Open Glyn.