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An interesting effect of deck archetype on "Drawn Winrate" percentages
I was recently reviewing stats for a few decks on HSReplay, trying to decide which build of my beloved Midrange Paladin to play tonight, when I noticed something odd about my deck.
As you can see in the link, every single card in the deck actually reduces the winrate of the deck when drawn (at time of writing, the winrate was sitting just below 61%, but for those unfamiliar with the site, you can judge relative winrates by the small arrows next to the percentages). This had me puzzled for a few minutes until I figured out what was going on.
Because the winrate of the deck is relatively high, and the deck aims to finish games in a reasonably short time span, the more cards you draw (roughly equal to the more turns that have passed), the less likely you are to win. Therefore, you are more likely to win the game than to draw any particular card from your deck - resulting in the seemingly strange behaviour.
With a few thought experiments, the effect ceases to seem so strange. For example, what if I played an "Ultimate Combo Deck" that wins 80% of the time on turn 1, but loses any game that goes to turn 2? The chance of having any particular card on turn 1 is quite low compared to the win rate (assuming a deck of 15 x 2 cards the odds are roughly 50/50), so in this deck every card will have a "drawn winrate" far below the average winrate of 80%.
You can check this yourself on the site. My reasoning forecasts that in decks that try to finish the game fast, most cards will have winrates below the deck's average, while in decks with a long game plan the effect is reversed, and most cards actually have a winrate higher than the deck's average. Two decks that showcase this effect perfectly are Highlander Priest and Pirate Warrior. It's also interesting to note that the sheer power of N'zoth's First Mate and Fiery War Axe are sufficient to overcome this effect.
Perhaps this is old news to many of you wonderful Redditors, but I personally had never thought about it before and thought it was unintuitive enough to share.
Iksar
Fun Fact!
Early on in figuring out how to best evaluate card power level, we made a pass through to see which were the most powerful cards in the game. In one of our first passes, we found that basically every control warrior card was showing up as extremely powerful even though the win percentage of the deck was around 50%. Similar to how you explained in your post, because control warrior as an archetype is much more likely to win the more cards that were drawn, it had an effect we didn't anticipate on power level statistics. When control warrior would win, they would draw 20-25 cards and all those cards would get a win. When they would lose, they would draw 7-12 cards and only those cards would get a loss. We corrected to now apply a statistical modification based on how many cards were drawn that game, but it was an interesting thing to learn.