How the score works

1. Recent ratings count more

A rating loses half its weight every 90 days. A rating from today counts fully, one from 90 days ago counts half, one from 180 days ago counts a quarter. Ratings older than 365 days are not counted at all.

2. Some accounts count less

• A rating from a cam.ac.uk account counts fully (1.0).
• A rating from a cantab.ac.uk account counts 0.75.
• If the account is less than 24 hours old, its weight is halved.
• If an account's last 10 or more ratings are all 1 star or all 5 stars, its weight is halved.
• Suspended accounts and our own test accounts count zero.

The weight of one rating is: 0.5^{(age in days / 90)} x account trust.

3. Few ratings are pulled towards the average

We add 10 imaginary ratings at the average of all colleges over the last 90 days. With only a handful of real ratings, a college sits close to that average. As real ratings build up, they take over. This stops one or two votes from putting a college at the top or the bottom.

score = (10 x m + sum of weight x stars) / (10 + sum of weights)

m is the average rating across all colleges over the last 90 days.

4. Who gets a rank

A college gets a rank only once it has at least 10 ratings in the last 90 days. Until then it is listed as "not enough ratings", with how many it has so far.

Scores are worked out again every time someone rates, and once every night. We show them to one decimal place, always next to the number of ratings behind them.