Over 60 million people live in the United Kingdom. How many of them train at least once a week in Brazilian Jiu Jitsu? Part 1

Over 60 million people live in the United Kingdom. How many of them train at least once a week in Brazilian Jiu Jitsu?

This question was posted by my good friend (and partner in crime!) Seymour Yang of the Meerkatsu fame. He tells me he has a guess but wanted me to devise a mathematical model to calculate a better guestimate. Not because I'm smart, but because I study statistics.

It took me a while to come up with the model but I like what it has come to:

"There is a ratio between how many purple belts and blue belts train at a BJJ club and how many white belts train at least once a week and I believe that, within a certain margin of error, that ratio is true for the majority of clubs"

That is my hypothesis. The correct way to go about checking it is to:

1. Choose a sample from the BJJ practicing population
2. Conduct a simple questionnaire
3. Plot the answers
4. Decide if any odd values are true or simply outliers.
5. Decide how exact I want my results to be (i.e. my margin of error)
6. Put the theory to the test.

If my theory proves to be true (within the error margins I set) then I simply calculate the number of white belts (which is my only unknown) and add them to the already registered blue, purple, brown and black belts in BJJ.

This post is titled "How Many People Train BJJ in the UK? Part 1" because I'm still working thru it! I sent out emails to 122 Brazilian Jiu Jitsu clubs around the UK asking them to approximate:

1. How many Purple belts train at their BJJ club?
2. How many Blue belts train at their BJJ club?
3. How many White belts train at their BJJ club?


At least once a week.

28 clubs replied which (anything about 20) is a good sample size.

I would like to share with you a quick graph of how many Blue belts train BJJ for every white belt:

Ratio of BJJ Blue Belts to White Belts

As you can see, the numbers do indeed fall within a relatively narrow margin, except for one value which I deem to be an outlier. I'm also glad to report that I got a very similar graph for the BJJ Purple belts vs BJJ White Belts:

Ratio of BJJ Purple Belts to White Belts

It's all looking good so far. More on number of people who practice BJJ in the UK soon.



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