#NewsBytesExplainer: How does IMDb calculate its ratings?
What's the story
Recently, the Internet Movie Database (IMDb) brought down the rating of the latest Hindi movie The Kashmir Files from 9.9-10/10 to 8.3/10 in a day. The movie aggregator site said this happened as they had employed an alternative rating mechanism after encountering "unusual voting activity" on the title. Many fans have alleged foul. So let us try to understand how IMDb ratings work.
Context
Why does this story matter?
Launched in 1990, IMDb remains to be one of the most widely known and credible sites for information on movies around the world. Further, people check out ratings of various films across different genres on IMDb's site to adjudge whether the movie is worth watching. Hence, the IMDb ratings can, at a stretch, build or break the credibility of a new release.
Details
IMDb doesn't calculate arithmetic mean of individual votes
First things first, users with registered IMDb accounts can rate a movie on a scale of 1-10. As per IMDb, "Individual votes are then aggregated and summarized as a single IMDb rating, visible on the title's main page." But the final rating isn't a simple arithmetic mean (that is, the sum of all votes divided by the number of votes) but a "weighted average."
Technique
What is weighted average? When is 'different weighting calculation' used?
So what's a weighted average? Here, votes by all users are considered but one user's rating might have more weight aka impact than some other user. "When unusual voting activity is detected, a different weighting calculation" is used, as was the case with Vivek Agnihotri's The Kashmir Files. IMDb keeps this alternate calculation method a secret, "to ensure that our rating mechanism remains effective."
Credibility
Are IMDb ratings accurate? Can these be wrong?
How accurate are IMDb ratings? The site says they do calculate movies using "a consistent, unbiased formula" with no human interference, thus, the numbers displayed next to a title are factually correct. But IMDb doesn't claim to be accurate in terms of qualitative perspective. This is to suggest that a movie can appeal to some while seeming disgusting to others.
Information
IMDb ratings and its fallacy
Although the system usually works, there are side effects when normal users rate. Dedicated fans can come together to uplift their favorite star/studio's work (Suicide Squad [2016]), whereas, a celebrity currently facing public wrath can get bombed with numerous 1-stars (Justin Bieber: Never Say Never).
Others
How do Rotten Tomatoes and Metacritic rank movies?
IMDb is joined by the likes of Rotten Tomatoes and Metacritic in the field of film/show rating. Both of these sites use critic reviews to rank a venture out of 100, though Rotten Tomatoes has a separate rating arena for user reviews. So, while we get critics' opinions on these sites, there is credibility. But a general viewer might not resonate with these rankings.