A PLB for the Chesapeake Bay? - Page 7 - SailNet Community
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post #61 of 74 Old 2 Weeks Ago
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Re: A PLB for the Chesapeake Bay?

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Originally Posted by Minnewaska View Post
I saw some arguing their point, by noting they’ve “never in 30 years”. We don’t practice most boating safety protocol, because likelihood of loss is high. We do so because the risk of death is high, if you lose the bet. That’s a very important risk management point to understand. Cheers.
This argument is also obviously silly because those who didn't make it 30 years aren't here to tell us about it, the ultimate selection bias!
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Re: A PLB for the Chesapeake Bay?

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This argument is also obviously silly because those who didn't make it 30 years aren't here to tell us about it, the ultimate selection bias!
No. You are making the even larger (numerically) error of assuming any accident or emergency is fatal. This is far from true.

For example, a large number of people fall in the water without PFDs. Although a high percentage of fatalities were not wearing PFDs, that does not mean a large percentage of the people that fell in died. I doubt it's even 1%. Same thing here. I indicated I have never had to cut something away with a knife under duress. That would have included reefs, overrides, mooring lines and many other possibilities that aren't remotely life threatening, only urgent. I found other ways to untangle them.

Another sort of bias is that only accidents with serious, bad outcomes are reported. I'm sure the USCG has no idea how many people have fallen in the water and them climbed out.
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Re: A PLB for the Chesapeake Bay?

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No. You are making the even larger (numerically) error of assuming any accident or emergency is fatal. This is far from true.

For example, a large number of people fall in the water without PFDs. Although a high percentage of fatalities were not wearing PFDs, that does not mean a large percentage of the people that fell in died. I doubt it's even 1%. Same thing here. I indicated I have never had to cut something away with a knife under duress. That would have included reefs, overrides, mooring lines and many other possibilities that aren't remotely life threatening, only urgent. I found other ways to untangle them.

Another sort of bias is that only accidents with serious, bad outcomes are reported. I'm sure the USCG has no idea how many people have fallen in the water and them climbed out.
What? I'm confused, where did I claim that every accident is fatal? I said no such thing. I only said that people who died are not here anymore..
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Re: A PLB for the Chesapeake Bay?

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What? I'm confused, where did I claim that every accident is fatal? I said no such thing. I only said that people who died are not here anymore..
No you are not. If the number of fatal accidents is accepted to be a very smaller percentage of the whole, a few fatalities have little effect on selection bias. This is mathematically obvious.

By comparison, 95% of the people on any PFD thread say they wear them, when USCG studies put the wear rate for 2018 at 6%. The people commenting on a thread are most often those that agree. Very common.

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Re: A PLB for the Chesapeake Bay?

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No you are not. If the number of fatal accidents is accepted to be a very smaller percentage of the whole, a few fatalities have little effect on selection bias. This is mathematically obvious.

By comparison, 95% of the people on any PFD thread say they wear them, when USCG studies put the wear rate for 2018 at 6%. The people commenting on a thread are most often those that agree. Very common.
You're talking about something different (in addition to putting words in my mouth). I said it's selection bias, you started arguing about the relative "effect" of it. When people say they've gone 30 years without wearing PDFs/helmets/seat belts or whatever and are totally fine that's selection bias. I'm just pointing out how that's just a meaningless comment. I said nothing about the "effect" of this on any statistical analysis, and have no interest in arguing that.
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Re: A PLB for the Chesapeake Bay?

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You're talking about something different (in addition to putting words in my mouth). I said it's selection bias, you started arguing about the relative "effect" of it. When people say they've gone 30 years without wearing PDFs/helmets/seat belts or whatever and are totally fine that's selection bias. I'm just pointing out how that's just a meaningless comment. I said nothing about the "effect" of this on any statistical analysis, and have no interest in arguing that.
[definition from statistics journal]

Selection Bias:

In survey sampling, the bias that results from an unrepresentative sample is called selection bias. Some common examples of selection bias are described below.


I'm just sayin' there is little selection bias due to fatalities, which is what you implied. Your words were "...because those who didn't make it 30 years aren't here to tell us about it, the ultimate selection bias!"

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Re: A PLB for the Chesapeake Bay?

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[definition from statistics journal]



Selection Bias:



In survey sampling, the bias that results from an unrepresentative sample is called selection bias. Some common examples of selection bias are described below.





I'm just sayin' there is little selection bias due to fatalities, which is what you implied. Your words were "...because those who didn't make it 30 years aren't here to tell us about it, the ultimate selection bias!"
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Re: A PLB for the Chesapeake Bay?

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I promise I will go swimming once the weather warms up and do a DSC test with the handheld. Have no interest doing that from the middle of the Bay but at least we'll have some data from close to shore
Well, we have a data point. Today I did not go swimming (don't like water temp yet) but I thought I try out the DSC test with the hand-held VHF just from the cockpit. I am 95% sure that I did that before and that it worked.

Not today! I let it 'ring' for several minutes and no acknowledgement!!!
Just to be sure I did nothing stupid, I 'called' my boat's VHF on DSC and it worked fine (for the sticklers for details: the boat VHF and handheld have different MMSI numbers, the latter is associated with my small boat which usually but not always saves as dinghy to the big one). I also did the DSC test using my main VHF and received an acknowledgment within 5 seconds or so. I did both tests (handheld and main VHF) several times, and each time the main VHF worked within seconds while the handheld never got an acknowledgment.

My conclusion is that EVEN FROM A BOAT a handheld cannot be trusted to send an emergency call in the Chesapeake. As I said, I believe that it worked before but my experiment today showed that it is not reliable. And, of course, I expect that transmission will be much worse from water level, rather than ~8' above it (cockpit).

So, a PLB is definitely in my future!
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Re: A PLB for the Chesapeake Bay?

"several times, and each time the main VHF worked within seconds while the handheld never got an acknowledgment."

Just to be clear, it is not that the handheld NEVER got an acknowledgement, but you are saying many/most times it did not get an acknowledgement?

Indicating perhaps a DSC problem in the VHF, not necessarily an issue of range of suitability for performance.

I'd suggest contacting the maker, in or out of warranty, to let them know you've just gotten around to testing this and it appears to be defective. The better brands will make an accommodation, as a customer courtesy, and often repair it or replace it.
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Re: A PLB for the Chesapeake Bay?

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"several times, and each time the main VHF worked within seconds while the handheld never got an acknowledgment."

Just to be clear, it is not that the handheld NEVER got an acknowledgement, but you are saying many/most times it did not get an acknowledgement?

Indicating perhaps a DSC problem in the VHF, not necessarily an issue of range of suitability for performance.

I'd suggest contacting the maker, in or out of warranty, to let them know you've just gotten around to testing this and it appears to be defective. The better brands will make an accommodation, as a customer courtesy, and often repair it or replace it.
The handheld NEVER got an acknowledgement. At least not the 5 or 6 times I did it yesterday. As I said in my post, I am pretty sure it worked when I tried it the last time, maybe two years ago?

I see, you say there may be a problem with the unit? As I said, I could make a DSC call to the boat's built-in VHF with no problem. Of course, I was ON the boat

Yes, perhaps I should contact the manufacturer. It is a Standard Horizon so I expect they should stand behind their product. Thank you for the suggestion
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