GraphScale of the Frequency Axis

Since bar graphs visually display information, the starting point and interval of the scale are very important. Choosing the scale is much more important than simply making the graph fit on the paper. The starting point and interval can be changed to make a graph look different, although the data it is presenting is actually unchanged. For example, scale can be altered to make bar heights seem dramatic or to make them seem insignificant.

We should take a more in-depth look at scale to demonstrate some of the things you should be looking for when evaluating a bar graph. The scale is determined by the range of values being represented. This means that the scale does not need to begin at zero.

Both graphs below contain the same information. Compare the two. Look at how the scale of the frequency axis can make a difference in the presentation of the information.

 Sales for Company X for the Fourth Quarter-1995 Sales for Company X for the Fourth Quarter-1995 Note the scale in the graph above: The frequency scale begins at 74 and ends at 82. This is because the range of values being graphed are from 77 to 82. Since we want our smallest bar to have some height, we started the scale at 74. If you look at bar heights, it looks like the ratio is 2:1. However, if you use the actual values, the ratio is then 82:77, which is not 2:1. Direct comparison of bar heights can only be made when the scale begins at zero. So why not begin all scales at zero? Note the scale in the graph above: The frequency scale with begins at zero. It is clear that the bars for Oct and Dec have nearly the same height. This means ratio of Oct. sales to Dec. sales is nearly 1:1 Having all bars appear nearly the same height makes it difficult to analyze any trends that may exist or to look at differences between months.