While doing research for an as-yet unreleased editorial on remakes and sequels, I gathered up a lot of box office data. Parsing the data, I labeled movies that were remakes, sequels, adapted, and original content, and I noticed a steady decline in the overall number of original movies that were in the top 20 box office earners. But revenue of original movies has held steady, despite that drop in the number of films in the top 20.
There are more original movies being made than 30 years ago thanks to independent features. Sequels, adaptations, and remakes are huge box office earners and it's easy to see why: people already know what they are.
Once I had everything organized, I thought this would make a great infographic. Having everything color coordinated allows you to digest lots of data by simply glancing over it. Box Office Mojo's data only goes back to 1980, so that's as far back as I could go. The data sets/years are every two to three years. If people really like it, I might do one that's every year and not just a sample of 15.
I've made the infographic available as a poster/print on Redbubble, and pricing varies on the size and options. Finally, you can see the raw/ugly spreadsheet data (here) and share your own conclusions in the comments.