This is a continuation - with modifications - of a test that started in https://phabricator.wikimedia.org/T121543.
We needed to modify the event logging in order to get reliable data to analyze.
Here's a list of issues with EL/data from the first run: T137158. In summary: 1. we didn't record if the clickthrough was on an interwiki result; 2. something funky is going on with the third value of the extra parameters field; 3. that third value needs to be explicitly 0 when the number of results returned is 0, rather than just missing.