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[pspp] / doc / language.texi

diff --git a/doc/language.texi b/doc/language.texi
index 0bab21289791056153577106549a3bf6b57aef21..1c9a4f0105245a5550f7ad71f577be5db2be0c53 100644 (file)
--- a/doc/language.texi
+++ b/doc/language.texi
@@ -509,7 +509,32 @@ Similar to print format, but used by the @cmd{WRITE} command
 
 @cindex measurement level
 @item Measurement level
-Nominal, ordinal, or scale.
+One of the following:
+
+@table @asis
+@item Nominal
+Each value of a nominal variable represents a distinct category.  The
+possible categories are finite and often have value labels.  The order
+of categories is not significant.  Political parties, US states, and
+yes/no choices are nominal.  Numeric and string variables can be
+nominal.
+
+@item Ordinal
+Ordinal variables also represent distinct categories, but their values
+are arranged according to some natural order.  Likert scales, e.g.@:
+from strongly disagree to strongly agree, are ordinal.  Data grouped
+into ranges, e.g.@: age groups or income groups, are ordinal.  Both
+numeric and string variables can be ordinal.  String values are
+ordered alphabetically, so letter grades from A to F will work as
+expected, but @code{poor}, @code{satisfactory}, @code{excellent} will
+not.
+
+@item Scale
+Scale variables are ones for which differences and ratios are
+meaningful.  These are often values which have a natural unit
+attached, such as age in years, income in dollars, or distance in
+miles.  Only numeric variables are scalar.
+@end table
 
 @cindex custom attributes
 @item Custom attributes