Question about a dot plot and the variables....

[grace0220]

Question: For a statistics project, a group of students wonder if there is a difference In the number of French fries two different drive-thru's serve. They randomly select a day and time to purchase five orders of fries from each drive-thru. They make a dot plot of the data and the label on the x-axis as "number of fries in one bag/order". There is one dot plot for each of the two drive-thru's. What is the response variable and the explanatory variable?

Why I'm asking: I was confused with this because if the explanatory variable is what you use and the response variable is what you predict, shouldn't the explanatory variable be the drive-thru and the response variable be the fries because you should use the drive-thru to predict how many fries you will receive? You can't use the count of fries to predict a drive-thru. The x-axis should be labeled always with the explanatory variable but you can't label the bottom of a dot plot with a drive-thru, it has to be count of fries. Looking for somebody to explain this a bit for me....

 

[Prof]

What you are saying makes sense. The explanatory variable is the input (independent) variable and the response variable is the output (dependent variable). You are correct that the input would be the number of the drive-in (1 or 2), and the output would be the number of fries in one bag/order.
In a bar graph (histogram), the bottom of the graph would have drive-in 1 and drive-in 2, and the vertical (y) axis would typically have the MEAN number of fries per bag in each drive-in. This would be a the more common display for the data and probably what you are imagining.

However, a dot plot is a different sort of display. It only has one variable on each graph so there really isn't an explanatory and response variable. Those terms would be used for the overall problem where you have two different drive-ins (as shown above).The single variable would be represented on the bottom (number of fries), perhaps 10, 11, 12, 13, 14, 15. Then above each number, you would place an x or a dot for each bag of fries that has that number of fries. So there would be 5 x's or dots on each graph (separate graphs for drive-in 1 and 2).