+@node CTABLES Summarizing Missing Values
+@subsubsection Summarizing Missing Values
+
+CTABLES treats missing values in categorical and scale variables
+differently. For categorical variables, in most cases values that are
+valid and in included categories are analyzed, and values that are
+missing or in excluded categories are not analyzed. (@xref{CTABLES
+Per-Variable Category Options}), for information on included and
+excluded categories.) The following chart, in which cells that
+contain ``yes'' indicate that a value is analyzed, and the notes below
+it give the exact rules:
+
+@multitable {@headitemfont{System-Missing}} {Included Category} {Excluded Category}
+@headitem @tab Included Category @tab Excluded Category
+@item @headitemfont{Valid} @tab yes @tab ---
+@item @headitemfont{User-Missing} @tab yes [*] @tab --- [+]
+@item @headitemfont{System-Missing} @tab n/a [#] @tab --- [+]
+@end multitable
+
+@table @asis
+@item [*]
+Exceptions: The ``@t{VALIDN}'' summary functions (@code{VALIDN},
+@code{EVALIDN}, @code{UVALIDN}, @code{@i{area}PCT.VALIDN}, and
+@code{U@i{area}PCT.VALIDN}), which only count valid values in included
+categories.
+
+@item [+]
+Exceptions: The ``@t{TOTALN}'' summary functions (@code{TOTALN},
+@code{ETOTALN}, @code{UTOTALN}, @code{@i{area}PCT.TOTALN}), and
+@code{U@i{area}PCT.TOTALN}, which count all values (valid and missing)
+in included categories and missing (but not valid) values in excluded
+categories.
+
+@item [#]
+System-missing values are never in included categories.
+@end table
+
+@noindent
+The following table provides another view of the same information:
+
+@multitable {Missing values in excluded categories} {@code{VALIDN}} {other} {@code{TOTALN}}
+@headitem @tab @code{VALIDN} @tab other @tab @code{TOTALN}
+@item Valid values in included categories @tab yes @tab yes @tab yes
+@item Missing values in included categories @tab --- @tab yes @tab yes
+@item Missing values in excluded categories @tab --- @tab --- @tab yes
+@item Valid values in excluded categories @tab --- @tab --- @tab ---
+@end multitable
+
projects / pspp / blobdiff