Clean Win Rate (CWR)

What is it?

Clean Win Rate is the win rate of a card against decks that don’t have that card.

When a card is very popular, it may play against itself fairly often. When a card plays against itself, it always adds 1 win and 1 loss to the total stats; this moves the overall win rate towards 50%.

The goal of CWR is to remove this effect, by only considering the stats against other cards.

CWR vs WR

You can think of Win Rate as the weighted average of:

• Win Rate against other cards
• Win Rate against itself, always 50%

This image shows how these two blocks of battles are averaged into the total WR, in green.

Normally, CWR would be almost the same as Win Rate (WR), except when the card's usage is exceptionally high; then CWR can be very different.

This is also the reason why CWR isn't important with deck stats, as even the most popular decks rarely have more than 1% usage. This is a significant contrast with some cards that have reached more than 50% usage.

This chart shows how CWR changes based on the Use Rate of a card. Each of the coloured lines represents a different standard Win Rate.

For all of the WR values, you can see that the change in CWR is very small when close to the vertical axis; i.e.: low usage. As card usage increases, the effect on CWR also does increase. At Use Rate values above 50%, the effect on CWR is significant.

Is CWR better?

Generally the answer is yes. For low usages, where it's not important, it will basically match WR values.

The main drawback is arguably that it introduces a new stat that may not be intuitive for uninformed users.

Calculating CWR

When source data is available, the ideal calculation method is simply to remove events in which the card plays against itself and recalculate Win Rate after that.

When sample sizes are big enough to create even distributions, it's possible to simply calculate CWR by knowing WR and UR. This alternative calculation assumes that the share of events in which a card faces itself is the same as the Use Rate of the card.

E.g.: If Golem is played in 10% of battles, Golem will also face Golem in 10% of battles.

Note: this simplification may not be appropriate wherever matchmaking isn't randomised.

With this simplification, the formula for CWR based on WR and UR is as follows: