How do you determine the scale of graphs?

Answer 1

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.

Answer 2

Sometimes you need to make an arbitrary determination of the scale you choose to display on a graph. In all cases, you would find the greatest and least values to be displayed on your graph, then decide on an interval that would divide the range of numbers into a manageable size (e.g. 1, 10, 100, etc.), then start the lowest value one range below the least value of your data and end with the highest value one range above the greatest value of your data.

Answer 3

Almost anything that the creator of the graph chooses.