Maybe single day move on acquisition announcement - ATVI up quite a bit on 1/18, MSFT down that day.
As an aside, the methodology says "We calculate the correlations between 2 securities on the daily closing values of the last 20 years. If one of the two securities has not been on the market for so long, we use all available prices to calculate the correlation." - hopefully the author means daily changes, not daily values, because otherwise everything is spurious.
As an aside, the methodology says "We calculate the correlations between 2 securities on the daily closing values of the last 20 years. If one of the two securities has not been on the market for so long, we use all available prices to calculate the correlation." - hopefully the author means daily changes, not daily values, because otherwise everything is spurious.