Histogram

A histogram is a type of bar graph that shows a distribution of a quantitative variable. The horizontal axis of a histogram does not have non-quantitative categories, but instead they have ranges, intervals, or classes with units of measurement of the variable.  

To make a histogram:

Step 1) First draw an x (horizontal) axis and a y (vertical) axis.

Step 2) Label your axes: the x axis should be broken down into uniform class intervals in units of with whatever the variable is being measured. The number of classes should be relevant to the range of data; the y axis is measured off in whole numbers beginning with zero and ending at whatever whole number is equal to or greater than the number of observations in a signle class interval. 

Step 3) Count the number of measurements that fall into the first class range and draw a rectangle with the height being the number of measurements and the width of a single class interval.

Step 4) Repeat step #3 until all of the measurements have been placed into a class interval.  Done and done.

Example: 320 college students had a GPA of 1.0 or less. Here is the distribution of their GPAs.

All the students with a GPA between 0.0 - 0.2 would be counted in the first column below, between 0.2 - 0.4 would be counted in the second column, etc. (*Note: the class ranges are equal to or less than. In other words, if the variable was exactly 0.2 it would be placed in the first column because 0.2 is equal to the class value of 0.2.)

Here is the histogram of this distribution:

Video sample of a different problem.