Dear Economist,

I receive vastly more invitations to speak than I can manage. Some will be very lucrative, some will be very interesting and some will be easy to do. Many, however, will be neither lucrative nor interesting nor easy to do. Invitations start arriving up to a year and a half beforehand and then with increasing frequency almost right up to the last moment. What is the optimal response strategy, assuming that I never pull out of engagements once accepted?

-- A prominent economist, London

Dear Sir or Madam,

Although you cannot guarantee that you will never regret accepting an invitation, you can optimise your diary simply enough.

First, combine ease, interest and your speaker’s fee into a single measure of what makes an attractive invitation. If you later find yourself impoverished, overworked or under stimulated, adjust that combination accordingly.

Then treat each slot on your calendar as a separate optimal experimentation problem. When an invitation arrives you will know from experience how attractive the invitation is and how many others are likely to materialise between now and the speaking date. If the answer is four, only accept an invitation that experience shows is in the top quartile: on balance, it’s likely to be the best you get. The closer you get to the speaking date, the lower you should set your standards for acceptance.

You should also maintain a “reservation price” below which you prefer free time - especially, I suggest, on your wedding anniversary. If you anticipate becoming more popular, you will expect more attractive invitations in larger quantities and should set higher standards. The converse also applies - so beware cut-price competitors. There are some smart young economists around, you know.

Tim Harford www.timharford.com

Questions to: economist@ft.com