Active Diver Statistics

[JohnAd]

The training agencies would be in the best position to get the information, ...

How would they know?

[Greenwood_60]

How would they know?

Sampling.

[JohnAd]

Sampling.

Who would they sample? How? PADI has in the past sent out surveys to new students via mail, getting far less than a 10% return. They are switching to email in the hope of increasing it to 15%. How much money would such a survey cost, and what would be their incentive to pay that money. How would they be able to get in touch with people who certified 40 years ago and are still diving but have moved 5 times without telling them?

This Wikipedia article lists well over 150 diver certification agencies around the world, and I know one that isn't on the list. Suppose they all did this. Who would put all that information together?

And suppose that actually happened. Suppose PADI, UTD, TDI, NSS-CDS, and PSAI all got in touch with me and asked me if I were still diving. Would I then be reported as one active diver or five active divers?

[Greenwood_60]

I think you're missing my point. They could take a random sample of their certified divers and get a reasonable representation of what percentage of certified divers continue to dive and for how long. They may already have. My point is, you and I will never see their numbers.

[PeterBuzzacott]

Divers are what is known in epidemiology as a "discrete" population, in that we aren't registered anywhere. The difficulty we face in determining a denominator is similar in researching the homeless, illicit drug users, same-sex relationships, basically any unregistered condition relating to health. If we had diver numbers, and/or dive numbers, then we could identify such things as the correct insurance premiums to charge, which sub-groups might be over-represented in injuries or deaths and ripe for safety interventions, and other practical things. But, we don't. There have been some good attempts. Warrick McDonald in Victoria, Australia surveying number of air-fills for a good while, telephoning all the dive centres in the state. Something similar was done in Canada and linked to mortality. At the US base on Okinawa they counted air-fills and injuries and deaths to determine morbidity and mortality per dive. DAN (USA) examined their insured member numbers and claims made.

I gave it a good go in Western Australia, trying multiple methods to build up a picture that could be used to "guestimate" approximate figures. These figures I hoped would give me Bayesian estimates to start with, before then using other sampling methods to test their robustness.

The methods I used were:
Firstly, I counted every dive centre advertisement in every telephone directory for Western Australia, since the first in 1969, (which had one ad). Growth was steady till 2000 and then it levelled off. Here is the reference: Buzzacott P. Western Australian dive industry growth and survival, 1969-2005. Journal of Ecotourism, 2008; 7: 221-229.
Next I did a survey of 500 dive centre customers including previous students and walk-in customers. From this I estimated how active the still active were and what the level of activity was by how many years since trained. That was published here: Buzzacott P, Pikora T, Rosenberg M. Post-training dive inactivity in Western Australia. Diving and Hyperbaric Medicine. 2008; 38: 137-139.
In doing my literature review for that study in 2004 I gathered a collection of data to give me some estimates of the possible scale of participation that I should expect in West Australia, which can be downloaded here: http://archive.rubicon-foundation.or...pdf?sequence=1
My next study saw me hanging around dive sites and crewing on liveaboard trips, surveying active divers about their experience, years of training, etc etc. One of the papers describing those results can be downloaded here: http://archive.rubicon-foundation.or...pdf?sequence=1

So, now we have an idea of how many dives happen each year in WA, how many the typical diver does, a ball-park idea how many divers actively dive each year and, out of them, how many will take next year off and how many will return to the sport after not diving this year. I also updated the telephone directory listings three years ago to see if the size of the industry appeared to have changed. We still don't have a census but we do have a better idea about the situation than we did when I started this full-time yen years ago.

The next step in the plan was to try alternative sampling methods to strengthen the level of evidence, by having multiple sources pointing towards the same figures. Snowball sampling is now easier than ever, thanks to social networking, but the one method I haven't managed to try yet is capture-recapture, like tagging fish. Basically, I could sample a large database, (let's hypothetically say Driver's licences), and pull out five identifiable items per person, like date of birth, address, maybe names, marital status or whatever, doesn't matter. Then we go somewhere else like surveying divers showing up for dives or members of dive clubs or anywhere totally unrelated to driver's licences but related to diving, and ask those exact same five questions, and from the percentage that are "recaptured" it is possible to estimate how many "divers" are in the wider population (in this simple example, the wider population who have driver's licences and who are in dive clubs).

[Minijunkie]

So, if there are about 3000 cave divers in the US... and 10% or so are women. Then, my girlfriend IS one in a million, just like I tell her.

[speleodiver]

Are all these "cave divers" certified? Seems to be a lot of uncertified ones lately. However, give it s month or tow and their numbers will be far lower! Just saying.

[Minijunkie]

I had a chance to talk about this subject with a NSS-CDS instructor trainer this past weekend. He said that the best guesstimates that the NSS-CDS have been able to conjure up after talking with the other training agencies would put the number of cave divers @ approximately 8,000 worldwide.


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