you would need to take the trends and growth data in there, normalize accordingly to a benchmark (can be the broad market, competitor, general volume in defi on mainnets/l2s/others), calculate historical volume rate of uniswap compared to that in period with/without incentives and in same/different market regimes, and finally infer how the volume would have been without the UEII program.
In general normalized data for different market regimes and for average market growth is what we need in any program to barely undertand even the effectiveness.