Polish the Brexit synthetic control example

[drbenvincent]

• Add in more explanation
• Add reference to similar work
• Add caveats
• Make the take home conclusion clearer. Get a plot of the cumulative causal impact at the latest point in the time series
• This would be a good example to specially showcase on social media

[pamant22]

Maybe this is very old now, but do you think it really makes sense to display or point toward cumulative GDP? Isn't GDP really a snapshot of the economic health of a country? If two countries have equivalent GDP today we don't consider the historics, we would say they are now equally strong economically (as measured by GDP). I'm no economist so I could be wrong.

Edit: In fact in the referenced article (https://www.cer.eu/publications/archive/policy-brief/2022/cost-brexit-so-far) they only appear to reference the snapshot current difference between actual and 'doppelganger':