Date:         Thu, 17 Apr 1997 17:01:55 GMT
Reply-To:     Edward Malthouse <ecm@NWU.EDU>
Sender:       "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From:         Edward Malthouse <ecm@NWU.EDU>
Organization: Northwestern University
Subject:      missings in Boolean expressions

It seems that sas treats missing values as being less than any number, e.g.,
 
data tmp;
  input x;
  if x < 10 then lt10 = 1;
  if x > 10 then gt10 = 1;
cards;
.
;
run;
 
proc print; run;
 
                           OBS     X    LT10    GT10
 
                            1      .      1       .
 
The expression ". < 10" is true.  Can anyone explain the rationale for this?
If we don't have data for something, how can we say that its value is less
than 10?
 
Thank you,
 
Edward Malthouse
Department of Marketing
Northwestern University
Evanston, Illinois
ecm@nwu.edu