work on missing value handling

[pspp] / doc / statistics.texi

diff --git a/doc/statistics.texi b/doc/statistics.texi
index adf1f67d95dac39ae5a6f8d04061c0874671867f..78b76bfbc492e2a1d48622ceb04f9bd629fd6e77 100644 (file)
--- a/doc/statistics.texi
+++ b/doc/statistics.texi
@@ -1242,6 +1242,12 @@ for each function is listed in parentheses:
 @item @code{COUNT} (``Count'')
 The sum of weights in a cell.
 
+If @code{CATEGORIES} for one or more of the variables in a table
+include missing values (@pxref{CTABLES Per-Variable Category
+Options}), then some or all of the categories for a cell might be
+missing values.  @code{COUNT} counts data included in a cell
+regardless of whether its categories are missing.
+
 @item @code{@i{area}PCT} or @code{@i{area}PCT.COUNT} (``@i{Area} %'')
 A percentage within the specified @var{area}.
 
@@ -1252,7 +1258,11 @@ A percentage of valid values within the specified @var{area}.
 A percentage of total values within the specified @var{area}.
 @end table
 
-The following summary functions apply only to scalar variables:
+The following summary functions apply only to scalar variables or
+totals and subtotals for categorical variables.  Be cautious about
+interpreting the summary value in the latter case, because it is not
+necessarily meaningful; however, the mean of a Likert scale, etc.@:
+may have a straightforward interpreation.
 
 @table @asis
 @item @code{MAXIMUM} (``Maximum'')
@@ -1292,10 +1302,23 @@ The standard deviation.
 The sum.
 
 @item @code{TOTALN} (``Total N'')
-The sum of total count weights.
+The sum of weights in a cell.
+
+For scale data, @code{COUNT} and @code{TOTALN} are the same.
+
+For categorical data, @code{TOTALN} counts missing values in excluded
+categories, that is, user-missing values not in an explicit category
+list on @code{CATEGORIES} (@pxref{CTABLES Per-Variable Category
+Options}), or user-missing values excluded because
+@code{MISSING=EXCLUDE} is in effect on @code{CATEGORIES}, or
+system-missing values.  @code{COUNT} does not count these.
 
 @item @code{VALIDN} (``Valid N'')
-The sum of valid count weights.
+The sum of valid count weights in included categories.
+
+@code{VALIDN} does not count missing values regardless of whether they
+are in included categories via @code{CATEGORIES}.  @code{VALIDN} does
+not count valid values that are in excluded categories.
 
 @item @code{VARIANCE} (``Variance'')
 The variance.