A note on rational call option exercise

Using Swedish equity option data, the rationality in the exercise of American call options is analyzed to see how well it complies with the theoretical exercise rules. Although the exercise behavior appears to be rational overall, several cases of both faulty exercise and failure to exercise are found. Almost a third of the early exercised calls are exercised at other times than predicted by theory. Several of these exercise decisions could potentially be explained by transaction costs, indicating that market frictions do affect the exercise behavior. However, over two thirds of the faulty exercises cannot be explained at all.