Cinemath: Do I Agree With IMDB Users? A Statistical Analysis of My IMDB Ratings

     November 27, 2011


I obsessively rate every movie I’ve ever seen on IMDB.  I started doing this when I was about 20 years old, so there are gaps between my memory of my adolescent viewing habits and this list.  But the record says I have seen 1,165 feature films, which must account for pretty much all of them.  At the very least, it’s a lot of data, and I’d like to do something with it for Cinemath, my semi-regular* feature that combines the wonder of movies with the tedium of mathematical analysis.

Since the list is stored on IMDB, every movie I rated conveniently has the public rating right next to it.  I am curious how often I agree with the public, and lucky for me, there are statistical tools to evaluate exactly that.  So after the jump, see how my ratings compare to those of the IMDB voting public, along with a few graphs of my viewing habits.

Props to IMDB, who made this a lot easier by allowing lists to be exported into .csv files with your rating, the IMDB average rating, runtime, and number of votes, among other categories.  I removed everything I’ve seen that has under 1,000 votes (sorry, Mongolian Ping Pong), which left 1,157 feature films in the dataset.

We’ll get to the good stuff soon, but first, indulge me in a look at my viewing habits.  The first graph is a histogram that counts the number of films I have seen for every release year since 1920.

Obviously there is a spike after I was, you know, born.  (In 1988, if that helps put 1,165 movies into perspective.)  A couple notes:

  • I haven’t seen more than 8 movies from any given year before 1979.
  • My biggest years are 2004 and 2009, each of which yielded 62 movies I have seen.
  • I think of 2004 as the movie I officially became a cinephile rather than just an avid moviegoer.  I have seen at least 50 movies from every year since 2004.

There are hundreds new releases every year, so there are absolutely gaps in my film knowledge.  But I am averaging over 50 movies for every year I’ve been alive, which seems respectable  for a part-time movie blogger.

The next graph breaks down the distribution of movies by runtime. (The notation [90,99] means “between 90 and 99 minutes.”)

I clearly like that 90-120 minute sweet spot.  Longer than an hour-and-a-half, shorter than two hours: over 60% of the movies I watched fall in this range.  I believe this is because most movies are between 90-120 minutes, but it’s also possible that I have a short attention span.

Now, on to the ratings.  For those not familiar with the IMDB ratings system: IMDB allows the user to rate any movie in the database from 1 to 10; the average rating across all IMDB users is given to one decimal point.  It is not a perfect system.  Wily users find ways to cast multiple votes to sway the rating.  Not all users use the 1-10 scale the same way (this will come up later).  And I must compare my single-digit ratings (i.e. “7″) to ratings with a decimal place (i.e. “7.3″).  However, the system in place is just fine for my needs.

The first graph here is a histogram that compares the number of times I have given out a certain rating to how often that rating is near the IMDB average.  For the purposes of the histogram, the IMDB average is rounded, such that everything between 6.5-7.4 is counted under “7.”

It is apparent that I consistently rate the movies I have seen lower than the IMDB average.  For comparison, my average rating is 6.06; the IMDB average for the same movies is 7.15.

To illustrate this difference further, I created a second graph that sorts the ratings from lowest to highest, and plots the results.

The “Brendan” line is always under the “IMDB” line until the very high ratings.  There are a handful of movies that I consider perfect 10s, while IMDB users have were unable to vote anything higher than The Shawshank Redemption and The Godfather, which sit atop the rankings with a 9.2 rating and over 1 million votes combined.  But otherwise, my rating pattern is much stricter.

The verdict is in, visually.  But to make it official, I called upon the Wilcoxon signed-rank test.  Essentially, the Wilcoxon test examines the difference (both sign and magnitude) between my score and the IMDB average for each individual movie, then evaluates whether the two sets of ratings are significantly different on the whole.  Indeed, the Wilcoxon test confirms that I rate movies about 1 point lower than the IMDB average.  The p-value is a statistical measurement between 0 and 1 that indicates how certain we can be a difference was truly detected.  The lower the p-value, the more certain the test.  The p-value for this Wilcoxon test was 0.000—so, there is no doubt.

I am not ready to brand myself an elitist, though.  So I looked at the numbers from a different perspective.  What if the average IMDB user and I feel the exact same about the quality of a movie, yet give it two different ratings because we view the rating system differently?** In other words, what if my “6″ is my “7″?

In an attempt to account for this, I looked at the standard score.  The standard score scales each rating relative to all the other ratings I have given.  The idea is that high positive values are assigned the movies I was crazy about and low negative values are assigned to the movies I hated, without being locked into the arbitrary 1-10 scale.  When the IMDB average ratings are also standardized, the standard scores (in theory) allow me to compare on a scale that strips that perspective influence.

You can see the results of the standardization below.  The first graph is another histogram that counts movies according the standard score given.  The second sorts the standard scores from lowest to highest, and plots the results.

Okay, that’s a little better.  I still give out more low ratings, but the lines in the second graph indicate a very similar standardized rating pattern.  The Wilcoxon test for the standardized data agrees: a p-value of 0.726 means a difference between my ratings and the IMDB average cannot be detected with any certainty.

One caveat: I am not totally sure that the standardization I used is valid for this data.  So I probably am an elitist.  Damn.  Well, at least if I am a movie snob, I have the movie histogram to back up my credentials.


*I was (and will continue to be) careful to say “semi-regular” in the first Cinemath article on the game theory of Snow White, published in May.  Emphasis on the “semi,” I guess, because I don’t know how often I am going to be doing these.  The researcher in me needs to focus on healthcare much more often than movies, but holidays are good for Cinemath.  In case you’d like to follow along, the next three are probably: 1) A look at the runtimes/ratings of Oscar Best Picture winners, 2) A year-end box office report, 3) A massive analysis on the impact of reviews/quality on box office that I started putting together in September before it swallowed me whole.


**This is how I rate:

  • 1 — This movie is reprehensible.
  • 2-4 — I did not like this movie.
  • 5 — This movie was okay, maybe enjoyable at times, but sometimes frustrating.
  • 6 — This movie was enjoyable, but somewhat forgettable.
  • 7 — This movie was enjoyable, and contained at least one standout element.
  • 8 — This movie was great, with many standout elements.
  • 9 — This movie was stellar, nearly flawless.
  • 10 — This is a pantheon movie, one that I have seen many times and will watch many times more.

Around The Web
  • Sal

    I feel you. I think imdb users are 12year olds and they only know number from 6-10. There are so many BAD movies that are rated above average. And eventually its not the fair coz on movie can be voted by 50.000 people, another by 10,000 and another by 1.900. So its not a fair comparison.

  • Edward Lee

    You’ve barely topped 1,000 films, and you have a gig writing for an entertainment website? Geesh. You demonstrate everything that’s wrong with the current state of journalism.

    • John

      I didn’t know there was a requirement of how many movies you needed to rate on IMDB to write for an entertainment website.

      •!/colliderbrendan Brendan Bettinger

        There is. It’s 3,000. I fudged the numbers on the application for my entertainment journalism license.

      • BobaFett

        I don’t know HOW you could in the business without seeing AT LEAST 10 movies from 1942:

        Pride of the Yankees
        The Glass Key
        This Gun For Hire
        Mrs. Miniver
        Yankee Doodle Dandy
        This Gun for Hire
        Woman of the Year
        Road to Morrocco
        Cat People
        Talk of the Town
        Holiday Inn

  • Nomis1700

    DAMN YOU Brendan Bettinger!!! Now I have an obsession too!!!!!!

  • Gavin

    Hahaha! Brendan I’m currently doing a masters in economic policy and we do a lot of this kind of data management so firstly, let me commend you’re utilisation of the Wilcoxian sign-ranked test but perhaps more importantly, you’ve got, what must amount to, less than a dozen movies that are rated as 10. Surely you’ve got to list your perfect dozen (or so).

    •!/colliderbrendan Brendan Bettinger

      I am hesitant to do so, but you’re right that I probably should. So with the preface that these are my favorite movies rather than which movies I think are “best,” this is what I’ve rated 10:

      The Shawshank Redemption
      The Lion King
      Band of Outsiders
      Stranger Than Paradise
      Toy Story
      Annie Hall
      Do the Right Thing
      Harold and Maude

      I think it’s pretty clear that I was a kid in 1994-95. Also, I’m the type who never checks “Strongly Agree” on surveys, so very few 10s.

  • Frederico Silva

    Just curious, what’s the movie you rated a perfect 10?

  • Magnus Rex

    This entire article is the definition of narcissism. A pure waste of Internet space. Useless.

    • Mr. Me

      Wow, that’s a bit harsh.

      If someone finds it interesting, something they can relate to, or entertaining, would you say it’s useless?

      P.S. I find the term “pure waste” to be an interesting one that warrants more rumination. (Not being facetious here, BTW.)

    • The Train!

      huh. interesting. this was one of the few articles i bothered to read at this site; usually i just scan the headlines. never can account for taste i suppose.

    • Agent_Black

      That’s funny, I thought the exact same thing about your comment, Magnus Rex.

  • kurjak

    How do you export imdb lists into .csv files with your rating, the IMDB average rating, runtime, and number of votes..??

    •!/colliderbrendan Brendan Bettinger

      At the bottom of the list, there is a link that says “Export this list.”

  • Mr. Me

    I think this is an amazing Collider article—it’s about movie watching/loving/assessing/rating/contextualizing, which is something any serious movie-goer can understand to some degree, and it’s a majorly refreshing departure from the daily movie news and rumors. Awesome. Wish there were more like this one to punctuate everything else. Great stuff.

  • excpired

    This was pretty interesting. I tried keeping a list of all the art I consumed but it got too tedious. I watch far more than 50 movies a year on average, some weeks I see upwards of a dozen in just a single week. I’d guess I watch at least 200 films a year, if not more. It is always a pain trying to go back and watch older films, but I’m getting the point where I have seen all of the post-70′s films and can start going back into earlier periods (once I stop torturing myself with new releases that are just terrible).

    However I don’t have a track record of working consistently so I have a lot of spare time. I am currently working full time and just to list what I can remember seeing this week off the top of my head for the first time: The Muppets, The Help, A Little Help, Cowboys & Aliens, Conan the Barbarian, Fright Night (2011), The Thing (2011), Race to World First. So 8 films this week, not a ton but that doesn’t even include the tv shows I watch.

    I’ll be plenty busy as well watching the 50 horror films collection I just purchased (though I’ve seen a few of them already).

  • Tarek

    Rating is all a matter of taste. I will rate David Lynch’s Dune 9, when others will give it 1.

    fortunately we don’t share the same tastes, nor we have the same sensitivities.

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  • Josephdj9

    I think the more movies you see, the lower you tend to rate movies in general, except for the “better” ones. What I mean is that the “better” movies tend to stand out if you see a lot movies.

    I totally agree with Tarek; rating is all a matter of taste. Did not really like Dune though :)

  • John123

    I also tend to rate movie lower than the average. I think Josephdj9 hits the nail on the head; the more movies you’ve seen the more conservative your ratings become (except for the better ones which you tend to rate higher than merited). What bothers me though is that a lot of movies are just plain over rated. To combat this I’ve devised a little formula to correct ratings: Average Rating * (1 – (Hated Review Count/ Total Review Count)). So for the obviously over rated “Children of Men” this would be 8 * (1 – (600/1123)) = 8 * 0.46571683 = 3.7. Granted this is a bit harsh but so is a pure 8 ;). I’ve also recently stumbled upon Picketee ( which tries to rank movies competitively, a much better approach in my humble opinion.

  • zetty

    Which tools did you use to make up the charts?

    Been interested to draw some from my votelist.. It’s so much statistics after all!

    Not only you can make a graph of what years have you been watching most — you also have each vote timestamped so you could make a chart to see when you have been watching the most movies, and what genres, and how did your taste had shifted.. Oh, and the countries chart would be most interesting too!

  • zetty

    Which tools did you use to make up the charts?

    Been interested to draw some from my votelist.. It\’s so much statistics after all!

    Not only you can make a graph of what years have you been watching most — you also have each vote timestamped so you could make a chart to see when you have been watching the most movies, and what genres, and how did your taste had shifted.. Oh, and the countries chart would be most interesting too!

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