doc: Describe how bin sizes are chosen for histograms.

diff --git a/doc/statistics.texi b/doc/statistics.texi
index 7a880d15ab33b17e9cf735de2fc2eb67ed4ba6ff..9cc49557ea2ff288b4abd32e57580bc1f68ae115 100644 (file)
--- a/doc/statistics.texi
+++ b/doc/statistics.texi
@@ -195,9 +195,13 @@ For instance, @subcmd{/NTILES=4} would cause quartiles to be reported.
 The @subcmd{HISTOGRAM} subcommand causes the output to include a histogram for
 each specified numeric variable.  The X axis by default ranges from
 the minimum to the maximum value observed in the data, but the @subcmd{MINIMUM}
 The @subcmd{HISTOGRAM} subcommand causes the output to include a histogram for
 each specified numeric variable.  The X axis by default ranges from
 the minimum to the maximum value observed in the data, but the @subcmd{MINIMUM}

-and @subcmd{MAXIMUM} keywords can set an explicit range.  Specify @subcmd{NORMAL} to
-superimpose a normal curve on the histogram.  Histograms are not
-created for string variables.
+and @subcmd{MAXIMUM} keywords can set an explicit range. The number of
+bins are 2IQR(x)n^-1/3 according to the Freedman-Diaconis rule.  (Note that
+@cmd{EXAMINE} uses a different algorithm to determine bin sizes.)
+Histograms are not created for string variables.
+
+Specify @subcmd{NORMAL} to superimpose a normal curve on the
+histogram.

 
 @cindex piechart
 The @subcmd{PIECHART} subcommand adds a pie chart for each variable to the data.  Each
 
 @cindex piechart
 The @subcmd{PIECHART} subcommand adds a pie chart for each variable to the data.  Each


@@ -289,6 +293,10 @@ normal distribution, whilst the spread vs.@: level plot can be useful to visuali
 how the variance of differs between factors.
 Boxplots will also show you the outliers and extreme values.
 
 how the variance of differs between factors.
 Boxplots will also show you the outliers and extreme values.
 

+@subcmd{HISTOGRAM} uses Sturges' rule to determine the number of
+bins, as approximately 1 + log2(n).  (Note that @cmd{FREQUENCIES} uses a
+different algorithm to find the bin size.)
+

 The @subcmd{SPREADLEVEL} plot displays the interquartile range versus the 
 median.  It takes an optional parameter @var{t}, which specifies how the data
 should be transformed prior to plotting.
 The @subcmd{SPREADLEVEL} plot displays the interquartile range versus the 
 median.  It takes an optional parameter @var{t}, which specifies how the data
 should be transformed prior to plotting.