Message-ID: <E2BCDE73F4D64D958A6E7D980A8125DE@gnat>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <555CCC21.4060901@gmx.com> <555E100C.25784.C7C6D2@mike.dennison.ntlworld.com>
Date: Thu, 21 May 2015 17:47:50 +0100
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Subject: Re: LF: MF 630m: False Decode or Real?
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Status: O

A couple of comments on the statistics......this has little to do with the 
decode process itself.

The timing only goes to show that the "decoded" call sign was active at the 
time NOT that he was really received, but might have been.

Graham thinks that because there were no more false decodes in the previous 
24 hours this one MUST be good. Statistics dont work like that ! If it is a 
million to one for a false decode you must expect at least near to a million 
decodes before another false one. On the contrary 2 questionable decodes of 
the same call would be extremely unlikely to be a random correlation so 
would provide good evidence the call was actually received and decoded 
properly. The probability of one true decode but not a second due to fading 
is very (very) low but not impossible.

Next though many do not seem to appreciate it, statistics dont "prove" 
anything, they provide a measure of the probability of an expected outcome. 
You determine both the probability of the expected outcome and also the 
probability it could be just random chance. The bigger the difference then 
the more likely the expected event occured. This is what makes a second 
decode so powerful.
People DO win the lottery every week! So false decodes do happen by 
chance.....but the same lottery winners rarely win two weeks in succession.

Alan
G3NYK


----- Original Message ----- 
From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, May 21, 2015 5:04 PM
Subject: Re: LF: MF 630m: False Decode or Real?


> Very likely a false decode. The clue is the two question marks. In my
> experience, almost every decode with question marks is false, and
> there are very few cases where these particular decodes are useful. I
> believe it would be helpful not to display these at all.
>
> Having said that, the deep search facility in Opera is very useful
> and has revealed some very interesting propagation information. But
> only using the decodes without the question marks which, again in my
> experience, are almost always genuine.
>
> Mike, G3XDV
> ===========
>
>> Just popped up at my RX:
>>
>> 17:52    477 VK3ELV de DF1VB/3 Op8 Deep Search ?? 16348 km -37 dB in
>> Dortmund with 140w + Top loaded L 18m vert 80m horz
>>
>> Any comments welcome
>>
>> 73, Jochen
>>
>>
>>
>> -- 
>>   -= DF1VB =-
>>   -= KH2MM =-
>> Jochen Althoff
>> +49 171 2020206
>>
>> "The wireless telegraph is not difficult to understand.
>> The ordinary telegraph is like a very long cat.
>> You pull the tail in New York, and it meows in Los Angeles.
>> The wireless is the same, only without the cat."
>> (Albert Einstein)
>>
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2015.0.5941 / Virus Database: 4347/9830 - Release Date:
>> 05/21/15
>>
>
>
>