Chart help needed: How to show proportion between two values?

January 16, 2013 6:48 AM

What type of chart do I want to show that one number is several times as many as another?

Putting a tall bar representing value x next to short bar representing value y shows that x is greater than y by x-y. (I realize that's a bit of an oversimplification.) What's the best way to show that x is greater than y by x/y times? I would love some examples.

Bonus question that I should really know the answer to: if x-y is the "linear" relationship, what is x/y? Neither the "geometric" relationship nor the "proportional" relationship sound right to me.

posted by Sock Ray Blue to media & arts (11 answers total)

You could take your bar graph, and label the axes in multiples of Y (rather than whatever the base units are).
posted by FrereKhan at 6:52 AM on January 16

It sounds like you want a logarithmic scale plot.

Here's a place to make such graph paper
posted by odinsdream at 7:00 AM on January 16

... if x-y is the "linear" relationship, what is x/y?

I would just call it the "ratio". I can't think of a phrase of the form "[foo] relationship" either.
posted by Johnny Assay at 7:15 AM on January 16

Calibrate this based on your intended audience carefully. A lot of people have trouble with logarithms.

I would design something that shows y filling x a certain number of times. kind of like if you were to visually represent "it would take 200 [or whatever] Rhode Islands to fill up the United States of America."
posted by entropone at 7:16 AM on January 16

Sorry, should have specified that my intended audience is pretty unsophisticated. Think USA Today reader.
posted by Sock Ray Blue at 7:19 AM on January 16

Do you need a graph for your audience?

For example, if x is 5.5 times bigger than Y, could you show 5.5 of something compared to 1 of the other in an infographic. Or just the text, like "1 : 5.5"

If you do have to use a graph, be aware that people tend to look at things by surface area and dimensions if it present. So if you want to show that x is 5.5 more than y then your surface area and height/size should reflect that. It is one reason why, thanks to the vagaries of Pi, circles are bad at showing proportional relationships.

I would also avoid logarithms. Generally an unnecessary complication where you're presenting to an audience.
posted by MuffinMan at 7:37 AM on January 16 [1 favorite]

Putting a tall bar representing value x next to short bar representing value y shows that x is greater than y by x-y.

Disagree. The ratio of the two items is pretty clear from such a plot, as long as your axes go all the way to zero.

The alternative is just to plot the ratio of the two items. You don't need or want any fancy type of plot. In fact, if you're only comparing two items total, I'd say you don't need a plot at all.
posted by kiltedtaco at 7:47 AM on January 16

... could you show 5.5 of something compared to 1 of the other in an infographic ...

Seconding this approach. They're called pictographs.
posted by ceribus peribus at 8:56 AM on January 16

You could do an area display like this radiation chart, where one area encloses the other. This immediately gets across the sense that something is X times bigger than something else.
posted by odinsdream at 9:54 AM on January 16

How about a bar graph with the larger bar divided into sections that are the same size as the smaller bar? You could also add a second y-axis that just has tick marks at intervals the same size as the smaller bar.
posted by alphanerd at 10:02 AM on January 16

Just had some more thoughts on this question. If you're looking at a bunch of different (x, y) pairs, you can say that x and y "vary directly" or "exhibit direct variation" if y/x is always a constant value. This is a special kind of linear relationship, one where the "y intercept" of the graph would be zero.

Over a bunch of different values, you could use the x axis to represent x, the y values to represent y, and the fact that they were related proportionally would be reflected in the fact that the slope of the graph is constant and that y is 0 when x is 0.
posted by alphanerd at 1:15 PM on January 16