Winrate difference is calculated relative to selected hero's win rate. Expected matches is calculated number of matches the heroes would be picked together randomly based on their pick rates. Deviation is difference between expected number of matches and the actual number (higher number is better and means the heroes are usually picked together intentionally, negative values mean otherwise). Percentage is how much of actual matches is the deviation number.

Higher Rank means that the pair of heroes is more effective together. Higher Rev-Rank means that the pair is frequently picked together, but has low efficiency.