http://www.ck12.org Chapter 2. Visualizations of Data
In this case the horizontal axis represents the variable (number of plastic bottles) and the vertical axis is the frequency
or count. Each vertical bar represents the number of people in each class of ranges of bottles (e.g.[ 1 − 2 ),[ 2 − 3 ),
etc.) We can see from the graph that the most common class of bottles used by people each week is the[ 6 − 7 )range,
or six bottles per week.
A Histogram is Not a Bar Graph!
Please avoid a mistake of beginning statistics students anddo notcall this a bar graph! As you will learn later, bar
graphs are only for categorical data. A histogram is for numerical data and most often will describe continuous data.
With histograms, the different sections are referred to as "bins" rather than "bars." Think of the column, or "bin,", as
a vertical container that collects all the data for that range of values.
Just like the frequency table, if a value occurs on the border between two bins, it is commonly agreed that this value
will go in the larger class, or the bin to the right. When students are drawing histograms, they sometimes make the
error of looking at the last value in the data and stop their horizontal axis at this point. In this example, if we had
stopped the graph at 8, we would have missed that data because the 8’s actually appear in the binbetween8 and 9.
Very often when you see histograms in newspapers, magazines, or online, they may instead label the midpoint of
each bin. Some graphing software will also label the midpoints of each bin unless you specify otherwise.
Histograms on the Graphing Calculator
To draw a histogram on your TI-83-family graphing calculator, you must first enter the data in a list. In chapter 1
you used the List Editor. Here is another way to enter data into a list:
In the home screen press2NDand then enter the data separated by commas (see the screen below). When all the
data has been entered, press2ND [STO]then2ND [L1].