Newsgroups: comp.software-eng
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From: adamksh@ip2020.Berkeley.EDU (Adam Kao (KSh))
Subject: Re: metrics and the SAT example
Message-ID: <1991May25.170939.22767@visix.com>
Sender: news@visix.com
Reply-To: adamksh@ip2020.Berkeley.EDU (Adam Kao (KSh))
Organization: Visix Software Inc., Reston, VA
References: <24563@unix.SRI.COM> <1991May21.223401.27023@netcom.COM> <1991May22.222646.10571@ico.isc.com> <1991May23.014904.5896@netcom.COM> <1991May24.192101.22317@grep.co.uk> <1991May25.053304.10445@netcom.COM>
Date: Sat, 25 May 91 17:09:39 GMT

In article <1991May25.053304.10445@netcom.COM>, jls@netcom.COM (Jim Showalter) writes:

[attribution lost]
>>It must be possible to establish credible causality too, otherwise you can't
>>be sure what you're measuring.  Say you notice that levels of ice-cream 
>>consumption correlate strongly with deaths at the beach.  Does this mean
>>ice-cream is a killer?

>Not at all. But it DOES mean ice-cream is a good predictor for beach-deaths,
>which was precisely my point. Thanks for providing another example to support
>my thesis! :-)

No.  Please, take the argument one step further.  Imagine that a
high-level committee is formed for the purpose of reducing deaths at
the beach.  Upon discovering the correlation above, the committee
promptly imposes limits upon the consumption of ice-cream.
Surprisingly, nothing happens.  (More likely, the committee acts in
late September, and then declares victory as beach deaths decline.)

We don't go around discovering correlations just for fun.  We usually
wish to draw conclusions about actions we should take to reach a
desired outcome.  We don't want software metrics just to predict when
our project will fail (as we stand helpless); we want to be able to
prevent a possible project failure.

What most people don't understand is that we must establish causality
before we can know what action to take.  Correlations do not establish
causality.


>>>My father pointed out one time
>>>that the statement "it only provides symptomatic relief" was stupid: if
>>>the symptoms of a broken arm are pain, bone jutting from muscle, and an
>>>inability to lift objects with the arm, then relieving those symptoms
>>>is the same as curing the problem--so what's the objection?

>>I take it your father wasn't a doctor, then? :-)  Taking Tylenol whenever
>>you have a headache doesn't cure your brain tumour.

>My dad was only pointing it out for broken arms. It doesn't work for
>everything.

This is exactly the point.  Now that you admit symptomatic relief
doesn't work for everything, you must show that symptomatic relief
does work for software.


Adam
