Price of Corn versus Quantity Demanded

Axes and their labels--The axes labels tell us what information is presented on each axis. One axis represents data groups is labeled Price per Bushel. The other axis is labeled Quantity Demanded. Bar--rectangular blocks that can have their base at either the vertical axis or horizontal axis. For this graph we can see that the base of the bars are on the horizontal axis. This means that the grouped data axis is the horizontal axis and the frequency axis is the vertical axis.

• Vertical axis--This axis is the frequency axis and contains the quantity demanded given in units of bushels.

• Grouped Data Axis--Since the grouped data axis is always at the base of the bars, the grouped data axis is the horizontal axis. The axis label tells us that along the horizontal grouped data axis we have the price per bushel, with each data group being a different dollar amount from $1 to $5. Two important pieces of information we must determine are the:

  • type of data being counted, and

  • how the data is grouped.

• Frequency Data Axis--The scale is the range of frequency values shown on the graph. The span of values represented is determined by the lowest and greatest values you wish to include on the graph.

When looking at this axis, look to see where the range begins and ends, as well as at the interval between tick marks. The vertical axis is the quantity demanded given in units of bushels. In this case, the frequency scale goes from 0 to 80, and uses an interval of units of 10. The frequency of our data groups range over nearly the entire scale so we are able to get a good picture of our data.

Analysis of the Bar Graph

Now that we understand all the pieces that go into a bar graph we are ready to discuss the analysis of a bar graph. As you can see, being able to do some data analysis of bar graphs can be more complicated then it initially looks. Keep in mind that parts of this process, such as doing an overview of the titles of the table and axes, are done quickly. The parts that may take more practice are determining the type of data groups being presented, whether the scale is appropriate, and making comparisons between groups of data. For example, in the bar graph Price of Corn versus Quantity Demanded, what information is being displayed in this bar graph?

Price of Corn versus Quantity Demanded

If we begin by looking at the axes we notice that the data groups are ordinal, going from a low of $1 to a high of $5. We also may notice that there does not appear to be any trend in going from low to high values of Price per Bushel. One thing we can see here is how difficult it can be to determine exact amounts from a bar graph. For example, at a price per bushel of $3, it is hard to tell whether the quantity demanded is 19, 20, or 21. While specific information of data groups may be difficult to determine, we can make a quick comparison.