Analyzing one categorical variable
Reading pie graphs (circle graphs)
For the past year, a travel agency has collected data about the number of individual tickets that it sells for its signature product, a Mediterranean cruise. The monthly data on ticket sales is shown below. What are the best and worst months for cruise sales? So what they have given us, this diagram. This is usually called a pie chart or pie graph because it looks like a pie that's sliced up into a bunch of pieces. Sometimes this is called a circle graph. But pie graph is much more common. And then they say it's monthly ticket sales. So each of these slices represent the sales in a given month. So for example, this blue slice over here represents the sales in January. And the way that a pie chart is set up, each slice is bigger or smaller, depending on what fraction of the whole it represents. So for example, they're telling us in January they sold 18% of the total year's ticket sales in January. So if you add up all of these percentages, it should add up to 100%. And not only do they tell us that they sold 18%, but the slice of this pie should be 18% of the area of the entire pie. It is literally 18% of the pie. If you were to eat this slice, you would have eaten 18% of the pie. Now with that out of the way, let's think about their questions. What are the best and the worst months for cruise sales? So the best month is obviously the month where they sell, where they have the largest percentage of their tickets were sold. And actually, I started with January, and if you just-- and this is what's neat about pie graphs. You wouldn't even have to look at the numbers, January just jumps out as the biggest slice of pie. If you didn't even see the numbers, if you couldn't even read, and you just looked at this and someone said what is the largest slice of pie? You would immediately say this is clearly the largest slice of pie right over there. And so that is actually the best month for cruise sales because they sold 18%. You see this 18% is larger than all of the other percentages over here. But it's clear, just by looking at the graph, this is the largest slice. Now what's the worst month for cruise ticket sales? Well, then we just have to find the thinnest slice of pie. And if we look over here, the slices of pie get pretty thin out down here. This is in the summer, in June and July, and in May. But the smallest are actually July and June. And this is where the numbers become useful. Because when you just eyeball it, you're not sure, hey, are these exactly the same? Or do they just look exactly the same? And that's where these numbers are valuable. And based on the data they've given us, it looks like these are tied for the worst in terms of ticket sales. In both of these months they sell only 3% in each month. So the worst months for cruise sales are July and June. July and June are tied for the worst. The best is clearly January, and then after January the next best-- they're not really asking us that, but since we have the pie chart in front of us, might as well ask ourselves that, what's the next best? Well it looks like November is slightly better than December. But in general, it's pretty clear that the winter months do much better in terms of cruise sales than these over here. And I guess people are looking to get away from the cold.