Since November 18, 2021, a new version of the ratings system has been in effect. You can read about the previous version in our blog.

All spare parts from brands that have a PR Score participate in the ratings (that is, those who have received at least 10 reviews).

Positions in the ratings are now determined by an algorithm. We use the Thomas Bayes algorithm to evaluate brand spare parts on a 10-point scale.

The algorithm calculates a Bayesian score using a special statistical technique. It considers not only the average rating given by users, but also the number of votes.

The algorithm uses the following formula: Ra = W R + (1 − W) R0. Where:

Ra = average (Bayesian) rating.
R = individual rating: average user score.
R0 = prior rating: the global average score for all items in our rating.
W = weight factor: it approaches 0 if there are few votes for an item, and approaches 1 if there are many.

Using this formula, the algorithm generates a rating like "9.99" for each brand's spare part that has a PR Score and at least 10 reviews.

The algorithm takes into account all reviews and votes included in the rating. Adding new reviews or votes for one participant may change the ratings of all other participants.

Auto Ratings

In the automotive rating, the score is calculated a bit differently.

First, it only includes votes from users who have specified their car make and model. Votes from auto rating pages are also taken into account.

Second, the score in the auto rating is calculated based on the total number of votes cast for all manufacturers of a spare part—not for each individual part or brand, as it is in the PR Score. To emphasize this difference, we display the % symbol in the auto rating.

For example, imagine there are 100 reviews for fictional CarAsist brake pads, and in 10 of them users specified Ford Focus as their car. This allows them to participate in the rating for Brake Pads for Ford Focus.

Let’s say three more manufacturers also participate in this rating and together with CarAsist brake pads they have a total of 100 votes. Out of these 100 votes, 25 positive votes (after subtracting negative ones) belong to CarAsist brake pads — meaning they lead the rating with a score of 25%.