This is a collection of responses to various questions I have been asked about the rating system I use on my reviews.
The -4 to +4 rating system was used for a long while in Cinefantastique, a magazine about fantasy cinema. They no longer use it but I and a number of people I discuss film with adopted it at that time or since. I like it because 0 indicates pure neutrality. If I am negative on a film, so is the sign of the number. Positive, the same is true. As I use it, it assumes film quality will follow a normal distribution curve. Each point away from zero corresponds to some part of a standard deviation (perhaps approximately half a standard deviation). By the time one gets out to +4 (or -4) the films are rarefied enough that these ratings include the entire tails of the curve. Further, because people have suggested to me that this system does not have enough granularity, about one third of films rated +2, for example will be dubbed "high +2", another third will be "low +2".
There are only a handful of films I have given a full +4 to, and quite a few get -4. There is some question in my mind as to whether the system could be destroyed by a film coming out that is miles better than anything I have ever seen in the past. I don't think that is quite likely, but it is theoretically conceivable that I might in the future want to give out +5s. I give a -4 to films that I consider are really completely worthless, and that does not happen all that often, but there are a lot more really bad films than really good. As someone pointed out, you can consider a rating point half a standard deviation.
Examples of ratings (highly subjective, and you can tell this list was made a long time ago):
0 is what I consider the mean for all films released. However 1 is probably the mean for all films I see in a theater. Since I try to avoid bad films when I am laying out money, the distribution of the films I see in theaters is skewed upward.
In general the differences in the various rating systems I consider much less important than a number of other factors. The most crucial is consistency in their application. Part of this is do not tie it to something that will shift a lot with time. For example, the dollar rating system -- "this film is worth $3 to see" -- will be good only until serious inflatiooon hits. It may not mean the same thing to a Canadian as it does to someone from the U.S. or to a rich person as a poor person. Unless the film industry gets considerably better or worse, a normal scale comparing against all films I have seen (like the one I use) is the least likely to suffer shifts with time.
It is also important that a scale is defined, particularly in the early days of its use, or when new people start trying to understand it.
A third important characteristic is granularity. Thumbs up vs. down is not very articulate. On the other hand I would feel very uncomfortable using a scale that rates films to four decimal places. Even assuming I was that sure I knew so precisely my feelings toward a film, I doubt that I could consistently apply such a scale. The real question is am I reasonably sure that I would give the same film the same rating a rear later, based on a viewing, not on memory of what I had given the film.
Each of these characteristics is in support of the most important characteristic, that you want a scale to communicate a general feeling about a film quickly. In my reviews the capsule serves that purpose, and the rating is like a capsule of a capsule.
I am periodically asked for a list of my +4 films. I don't have a fixed list in my head, but I would probably say (in no particular order after the first three, and leaving out fantasy films, which I admit I tend to rate too high):
If I am to include fantasy films I would add