ABT/ABBV—If you want to own both companies, you may as well buy now insofar as the combined share prices will likely to be higher at the split than the current share price. If you want to own only one of the successor companies, buy in January—or on a “when-issued” basis in December after such shares begin trading.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”