The reason why is that you can’t make any money just selling to the sub-population in many cases. Yes you are right that you can design the trial to identify t

The reason why is that you can’t make any money just selling to the sub-population in many cases. Yes you are right that you can design the trial to identify the sub-population that the drug works in. Sometimes drug companies do do this, but if they are going to go down this path they normally run a tighter Phase 3 trial and then try to expand post-approval by running more trials. It is all a cost/benefit analysis taking into account the patent life and lots of other commercial factors. The point I was making is that a high failure rate at Phase 3 is to be expected given the marketing needs of the company. A Phase 3 trial is not just a scientific exercise in proving a drug works, it is a complex balancing act where commercial concerns are critical.