Not sure, it's hard, since we seldom have randomised controlled experiments here.
Perhaps try looking for natural experiments, eg compare between countries, or between different sectors.
(Sometimes there's also silly legislation you can exploit for statistics, like the Onion Futures Act (https://en.wikipedia.org/wiki/Onion_Futures_Act) which can help to see the impact of futures trading on commodities.
Perhaps there's some corner of the pharmaceutical market that wasn't hit or was less hit by the Pure Food and Drug Act?)
