My goof

In my recent post on pharmaceutical regulation I wrote:

In the pharmaceutical market the major costs are all fixed costs (they don't vary much with market size) so profit =P*Q-F. Acemoglu and Linn look at changes in Q but a 1% change in P has exactly the same effects on profits, and thus presumably on R&D, as a 1% change in Q.

But as Bernie Yomtov pointed out to me a reduction in P will increase Q. Ugh, an economist who has to be reminded about the law of demand. Embarrassing. The argument goes through if demand is quite inelastic which makes sense for a lot of drugs given that the price to the final consumer is low to begin with due to insurance - nevertheless the result is not so clean. Indeed, because of the envelope theorem a small change in P will have only a very small change in profits. Sadly, I teach this to my students regularly. Did I mention that I have had the flu this week?