*2.1.1
Histogram*

The word histogram comes from the Greek *histos*, meaning pole or mast,
and *gram*, which means a chart or graph. Hence, the direct definition of
Histogram is Pole Chart. A histogram is used to display the distribution of
data values along the real number line. It is a traditional way of displaying
the shape of data and competes with the probability plot as a method of
assessing normality.

Histogram is a graph of the frequency distribution in which the vertical
axis represents the count (frequency) and the horizontal axis represents the
possible range of the data values. It is constructed from a frequency
distribution, where choices on the number of classes and class width have been
made. These choices can drastically affect the shape of the histogram With
GRAPHID, however, the number of classes can be increased or decreased
interactively to visualize the effect of changing the class intervals. The
ideal shape to look for in the case of normality is a bell-shaped symmetrical
distribution. If the histogram does not look like a (nearly) bell-shaped
distribution, one can standardize the variables and plot again the histograms
to explore whether standardization yields the expected results. Standardization
can be done within the module itself.

GRAPHID offers the possibility of viewing histograms of a number of
variables, one after another. The number of class intervals can be increased to
approximate a histogram to a probability plot.