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Re: Second PhD???
Only two of those -Pavoni and Hou- actually have multiple PhD's (and I agree with you, I have no idea why they did it). The others started PhD's at one university then moved to higher ranked university after the 2nd or 3rd year, which usually entails restarting the program, and is not a move that I would recommend without an advisor at the current program specifically advising a student to do so.
Originally Posted by ahududu
To answer the OP's original question, I have come across a number of people with multiple PhD's in finance or other business fields, but it is almost always someone who did a PhD in a STEM field (most often physics or engineering) but at a lower ranked university, ended up doing business or econ related work and decided to use their newly developed business interests as a way to get into academia by doing a business PhD.
To build on what startz commented, if you only got into a 50-70 econ PhD program, why would a significantly higher ranked business, stats, math or policy PhD program take you? And if it were an equivalent or lower ranked program, what would you gain? If anything the academic job market is much tougher in math and stats and tacking on a low ranked math or stats PhD will not help you on the econ job market. And most business or policy PhD programs will not take someone who already has an econ PhD because it is considered too close a field.
If you really truly have interests in business or policy and don't only want to do business or policy because you think the academic job market is easier (and for most business PhD's it definitely is) then maybe you should think seriously about your interests now and consider re-applying to business or policy PhD programs this cycle so you can switch over to those fields before you have spent too much time on your econ PhD. But this only makes sense if you truly feel you have interests in those areas not just because of an easier job market.