NOTICE This rating system has been downgraded based on some feedback. The gist of the change makes this a simple information system. We now calculate and publish only the hourly cost for the total time, lessons plus dancing, as well as the minimum root mean square distance between couples based on the size of the dance floor and the average attendance. Combining the previous weighted ratings using the geometric mean was confusing to visitors, so it has been eliminated. The scales are no longer ratings. The are provided figures and calculated relations in these provided figures. 
I've been trying to come up with a dance rating system that is relatively objective. There are many subjective aspects to consider that do not lend themselves to easy quantification. As a result of my somewhat unpleasant experiences with the dances at Mass MoCA, I have hit upon a couple of different numbers that can be used to compare dances. These numbers include the pricetime value, simply what it cost on a perhour basis, as well as the minimum average distance between couples, in feet.
This system does not rate such subjective factors as whether the dance features live bands or CD music, whether the music is well planned and varied, if requests are played, the general friendliness of the people who attend, the degree to which they pay attention to dance floor etiquette, how far one has to travel, whether the dance encourages attendance by individuals as well as couples, etc.. Bear all this in mind when you compare the cost and space factors.
One measure is the "value" of a dance  how long you get to dance for what price. This calculation begins with the concept of how much dance time is available for the price. Lessons are a nice addition and contribute to the value of the dance for some of us, but I'm assuming that we go to dances to dance. The majority of lessons that are given with dances I've attended benefit primarily the beginners or novices. For most of us, the value of the dancing is more. Logic dictates that any such rating should go up as the time available is longer and go down as the price goes up. In other words, the "value" of a dance should be directly proportional to the time available for dancing (and lessons) but inversely proportional to the cost. Instead of confusing readers with this inversion, I've chosen to us a much more familiar concept, the hourly rate. This measures how "expensive" your dance time is. To make it simple, I've simply added the lesson time and the dance time and divided the admission price by the sum of the lesson and dance time included in that price. Discounted prices are not used in this calculation. Only the adult, public, nonmember, "at the door" price of admission is used in this calculation. If you've got a discount price, you can calculate your hourly rate by dividing your discounted price by the total number of hours between the start and end times.
Another rating measure is the "dancability" of a dance  how much space there is to dance in for the people who are dancing. This rating criteria is based upon how "uncrowded" the dance floor is. To compute this rating I use the area and the "popularity" (average attendance). From these figures I compute the average distance between couples  how much room you have to move in. The actual formula for this is rather complex, because it involves finding out how many compact circles will fit in the danceable area, accounting for the spaces between the circles, and computing the resulting diameter of those circles. The diameter of the circle is the same as the distance from center to center. Since a couple in hold has a diameter of about 3 feet, subtracting that from the diameter of the space circles based on attendance gives the average distance to the next couple. (I measured my wife and myself together.)
The higher the number the better the rating. Larger numbers are better for Quickstep and Tango; smaller numbers are acceptable for Latin or spot dances. This measure does not take into consideration the fact that not everybody dances every dance. The percentage of people that sit out a dance varies with the kind of dance music as well as the character of attendees. Waltzes, Fox Trot, ChaCha, and Swing are quite popular at most ballroom dances. The popularity of Hustle and Salsa varies with the local. Quickstep is much less well known, and there's generally a much larger percentage of people who watch rather than participate  as a result, it tends to be featured much less or not at all in many places. In some places, patrons will do swing to a quickstep and will prevent quickstep aficionados from dancing by blocking the lanes. If you dance the Paso Doble, chances are you'll have the dance floor to yourselves in some areas (provided you can get the host to play one). Consequently, this rating number represents an overall measure of how uncrowded the dance conditions are at worst case  with everybody dancing. This number can also be exaggerated when the dance sponsors underreport attendance figures or fail to exclude the space taken up by tables and seating.
The rating system only measures how much time and space you get for your money.
It does not measure subjective factors.
