Which would you compare?

Did you know that the way data is presented affects the type of comparisons the audience can make? Let's take a look at a couple of examples to see which comparisons we can make and why.

Which comparisons are easy in each of these stacked bar graphs?

 

In both graphs, it is easy to compare the total number of penguins across the three years.

You'll also notice that it is easy to compare the bottom section of the stacked bar in each year. In the first graph, this represents Gentoo penguins. In the second graph, this represents Chinstrap penguins.

However, it is not easy to compare the middle or top sections of the stacked bars over time. This is because the baseline of these two sections vary depending on the height of the bottom section.

So, if you're going to use a stacked bar graph, make sure you put the part that you want your audience to compare at the bottom. And remember that they will only be able to compare the total height and the height of that bottom section accurately.

Which comparisons are easy to make in these two grouped bar graphs?

 

In the first bar graph, the bar representing the number of penguins is given a color based on the species, and the bars are grouped together by year. This makes it easy to compare the species to one another within a single year but hard to compare a single species across years.

In the second bar graph, each bar is given a color based on the year, and the bars are grouped together by species. This makes it easy to compare the number of penguins of a single species across the years but hard to compare species to each other.

For this type of data, a line graph is probably a better choice than a bar graph because it would allow us to compare both the species to each other and across time. But when you don't have time-based variable, think about what comparisons you want your audience to be able to make and group your bars accordingly.

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