Date: Tue, 5 Jan 2010 10:50:25 -0500
Reply-To: Peter Flom <firstname.lastname@example.org>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Peter Flom <peterflomconsulting@MINDSPRING.COM>
Subject: Re: New Comparison Operators? - WAS: missing numerical values = -
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>"Jonathan Goldberg" wrote
>> This is a hoary question. Logically speaking, having x < 2500 resolve to
>> true when x is missing is absurd, and having x = y resolve to true when
>> both x and y are missing is ludicrous. Missing means "I don't know." If
>> x and y are heights, you are claiming that you know that two heights are
>> equal when you don't know what either of them is.
>At the risk of seeming the fool, I've always thought of it as:
>if X = "I don't know" and y = "I don't know" then x does equal y.
Hmmm... paraphrasing Bill Clinton
"It depends on what your definition of equals equals". :-)
In the example Jonathan used, a person might not know their height, but probably knows it approximately.
A person who thinks she is about 5'1", but says "I don't know" because she isn't sure, maybe she's 5'0", does NOT equal a man who thinks he's 6'2", but might be 6'1".
Of course, that's a little silly, but it's easy to come up with much less silly examples.
On this, I like the R method better. If you ask if missing = missing, you get missing.
Peter L. Flom, PhD
Website: http://www DOT statisticalanalysisconsulting DOT com/