See, I've been tracking the total number of movies I've seen since 2005, but I've only been tracking the number of minutes since the start of 2010 (when I saw UP IN THE AIR and decided the movie watching equivalent of 10 million miles is 1 million minutes). But rather than start at zero I allowed myself to start with the time I've spent watching movies since I started tracking them.
At first, I estimated 90 minutes per movie (feature length program, be it a feature, a program of shorts, or a short + feature). I figured that was low, and I was okay with underestimating my total minutes.
But always, in my free time, I would look back at my records and calculate the totals for previous years. Some time back I finished finding the running time for everything I saw in 2009. It turned out my average time/movie in 2009 was just over 97.5 minutes. So I did two things to adjust my estimate of the total minutes. First, I included the actual running time instead of an estimated time for 2009. Second, for the movies prior to 2009 I used my 2009 average of 97.51126 as the estimated time/movie.
Well, I've just finished calculating the total running time for 2008. And I've updated my calculation in a few ways:
First, of course, I'm using actual values for everything from 2008 on. As of today, that's 1663 movies (feature length programs) with a total running time of 160,804 minutes, for an average of 96.69512928 minutes/movie.
Second, I've updated my estimate for pre-2008 movies using this average. That's 995 movies for a total estimated running time of 96,212 minutes (rounded off).
Third, and most importantly, I've automated the calculation of a new average time/movie based on every new running time I enter into my records. This is the most important part because it means when I add a movie and a running time, it doesn't just add to my total minutes. It also recalculates my estimate of pre-2008 movies. So if I see a film with a higher than average running time, not only are those minutes added to the total but the average goes up and adds even more to my total. The converse, of course, if I see something below the average running time.
In the meantime, I will, of course, continue to find more accurate records of the minutes I've spent watching movies pre-2008.
I'm posting this because I'm sure you all really come to my movie review blog to read about math.
A few side notes:
- 2009 actually had my highest average running time of any year I've calculated so far
- 2011 is pretty far below average, currently at just 96.092. That might not seem like much, but a half minute over the course of 400 movies is quite a bit. Especially odd since I've had some 4+ hour epics in there.
- Even with looking up the running times for everything, there is still some guesswork. Occasionally movies have different versions in different festivals or different countries, and vary by a few minutes. More importantly, a lot of silent films don't have set running times, since the projection speed was variable. I do my best to estimate and have noted the ones which I haven't found a listed running time. In general, my rule of thumb if I don't know is to give a silent film 10 minutes per reel. I think this is actually a pretty drastic underestimate, and that is intentional. I'd rather undercount than overcount.