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From: Ron <rjpeace(at)earthlink(dot)net>
To: Michael Stone <mstone+postgres(at)mathom(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: SCSI vs SATA
Date: 2007-04-06 16:41:25
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
At 09:23 AM 4/6/2007, Michael Stone wrote:
>On Fri, Apr 06, 2007 at 08:49:08AM -0400, Ron wrote:
>>Not quite.  Each of our professional 
>>experiences is +also+ statistical 
>>evidence.  Even if it is a personally skewed sample.
>I'm not sure that word means what you think it 
>means. I think the one you're looking for is "anecdotal".
OK, let's kill this one as well.  Personal 
experience as related by non professionals is 
often based on casual observation and of  questionable quality or veracity.
It therefore is deservedly called "anecdotal".

Professionals giving evidence in their 
professional capacity within their field of 
expertise are under an obligation to tell the 
truth, the whole truth, and nothing but the truth 
to the best of their knowledge and 
ability.  Whether you are in court and sworn in or not.
Even if it's "just" to a mailing list ;-)

1.pertaining to, resembling, or containing 
anecdotes: an anecdotal history of jazz.
2.(of the treatment of subject matter in 
representational art) pertaining to the 
relationship of figures or to the arrangement of 
elements in a scene so as to emphasize the story 
content of a subject. Compare narrative (def. 6).
3.based on personal observation, case study 
reports, or random investigations rather than 
systematic scientific evaluation: anecdotal evidence.

+also an·ec·dot·ic (-d t' k) or an·ec·dot·i·cal 
(- -k l) Of, characterized by, or full of anecdotes.
+Based on casual observations or indications 
rather than rigorous or scientific analysis: 
"There are anecdotal reports of children poisoned 
by hot dogs roasted over a fire of the [oleander] stems" (C. Claiborne Ray).

While evidence given by professionals can't be as 
rigorous as that of a double blind and controlled 
study,  there darn well better be nothing casual 
or ill-considered about it.  And it had better 
!not! be anything "distorted or emphasized" just 
for the sake of making the story better.
(Good Journalists deal with this one all the time.)

In short, professional advice and opinions are 
supposed to be considerably more rigorous and 
analytical than anything "anecdotal".  The alternative is "malpractice".

>>My experience supports the hypothesis that 
>>spending slightly more for quality and treating HDs better is worth it.
>>Does that mean one of us is right and the other 
>>wrong?  Nope.  Just that =in my experience= it does make a difference.
>Well, without real numbers to back it up, it 
>doesn't mean much in the face of studies that 
>include real numbers. Humans are, in general, 
>exceptionally lousy at assessing probabilities. 
>There's a very real tendency to exaggerate 
>evidence that supports our preconceptions and 
>discount evidence that contradicts them. Maybe you're immune to that.

Half agree.   Half disagree.

Part of the definition of "professional" vs 
"amateur" is an obligation to think and act 
outside our personal "stuff" when acting in our professional capacity.
Whether numbers are explicitly involved or not.

I'm certainly not immune to personal bias.   No 
one is.  But I have a professional obligation of 
the highest order to do everything I can to make 
sure I never think or act based on personal bias 
when operating in my professional capacity.  All professionals do.

Maybe you've found it harder to avoid personal 
bias without sticking strictly to controlled 
studies.  I respect that.  Unfortunately the RW 
is too fast moving and too messy to wait for a 
laboratory style study to be completed before we 
are called on to make professional decisions on 
most issues we face within our work
IME I have to serve my customers in a timely 
fashion that for the most part prohibits me from 
waiting for the perfect experiment's outcome.

>Personally, I tend to simply assume that 
>anecdotal evidence isn't very useful.

Agreed.  OTOH, there's not supposed to be 
anything casual, ill-considered, or low quality 
about professionals giving professional opinions within their
fields of expertise.  Whether numbers are explicitly involved or not.

>This is why having some large scale independent 
>studies is valuable. The manufacturer's studies 
>are obviously biased, and it's good to have some 
>basis for decision making other than "logic" 
>(the classic "proof by 'it stands to reason'"), 
>marketing, or "I paid more for it" ("so it's 
>better whether it's better or not").
No argument here.  However, note that there is 
often other bias present even in studies that strive to be objective.
I described the bias in the sample set of the CMU study in a previous post.

Ron Peacetree 

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