Histograms

Histograms look like bar charts but are meant to be used with measurement data.  The X axis represents values of the variable.  The Y axis represents the number of cases in the range of any given bar.  Histograms can be used to diagnose problems with distributions, but they are also the only display for measurement data that is easily read but unsophisticated audiences.

The histogram above displays grade point averages among a group of students.  Each bar is .25 of a grade point wide.  The first bar covers all GPAs from -.125 to .125.  The next bar covers .126 to .375.  I can change these bars to cover wider ranges.  For example, I could make the bars each .50 of a grade point average.

The thinner the bars of the histogram, the more detail about the distribution can be seen.  The thicker the bars, the more the "big picture" is emphasized.

SPSS instructions