I am writing a research article involving movies, and I want to prove my point that the movie industry is a very risky business. For this, I would like to quote a reliable source indicating the percentage of movies that make a net loss during their theatrical run. Let's restrict it to the American movie industry for the sake of traceability, and also only to movies that get a theatrical run in the first place.
I will assume that a net loss means that the production budget + advertising budget have not been retrieved in revenues (in theaters; DVD sales etc. make things more complicated again).
I remember having read somewhere on the internet, about two years ago that this number is 75%, but I cannot find this information anymore. It is not easy to find on the websites of MPAA, box office mojo, the-numbers dot com, imdb or rotten tomatoes, though I only had time for superficial searches.
I am aware that it is hard to say exactly. Any similar type of figure demonstrating the volatility of investments in the movie industry would also do, as long as it is from a reliable source (e.g. MPAA).