The rating system is determined by the combination of two factors: activity and popularity.
Activity Factor = 42%
Writing reviews (28%)
Writing follow-up reviews (4%)
Answering questions on your reviews (2%)
Posting comments on the reviews of other contributors (2%)
Creating new discussions (2%)
Making posts in discussions (2%)
Time in community (2%)
Review activity reflects the ratio between the number of your reviews relative to the average maximum of reviews between the top contributors. Verified reviews count exactly as much as unverified reviews. There are no limits on the number of reviews and follow-up reviews.
Only the past 360 days of activity is considered in Activity Factor.
Popularity Factor = 58%
Average review usefulness determined by votes (34%)
Average editorial vote (4%)
Number of comments on your reviews (9%)
Number of ratings on your reviews (9%)
Number of discussion posts from other contributors on the discussions created by you (2%)
We consider voting on your own reviews an inappropriate practice. The reviews should be evaluated by other people, not by the author of the review.
These factors are calculated daily, and in comparison to other reviewers (which is why your rating might change even if you haven't done anything).
There are several ways to boost your rating, like writing more reviews, follow-ups, commenting on others' reviews and posting on the forum.