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Dot Plots

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Hi. This tutorial covers Dotplots. So let's start with some data.

A group of 15 employees were asked how many siblings they have. The employees decided whether or not to count half-siblings or step-siblings themselves. And the following data was recorded.

So 0, meaning they had no siblings. 2, they had 2 siblings. 0, 2, 4, et cetera. So you have 15 data values.

So what we want to do is, since this is just raw data, we want to be able to display that using some sort of graph. So when a quantitative data set, so a numerical data set is small and the values are relatively close together, a dotplot can be used to display the data set. So if we look back at the data, notice we have 15 values, so not tons of data. And it's not very spread out.

Our smallest value is 0, our largest value seems to be 7. So not a huge spread in your data set. So we're going to use a dotplot. And a dotplot is a graph where one axis is drawn for the different values, and each observation is marked with a dot. Dots are stacked when a value is repeated.

OK, so we're going to make the dotplot. And let's actually try to get the data on here too. OK. So again, we need to make an axis, so I'm going to go ahead and do that here.

OK, so I'm going to use a ruler to get a nice straight line, and I'm going to use up most of my paper here. OK, and then I'm going to start marking off my values. OK, so starting at 0 and I'll just come by 2's like so.

And now what I'm going to do, make sure that when you're drawing a dotplot that you leave some room above your dotplot like I did here. So now what I'm going to do is figure out how many. Basically, what's the frequency of each of the values that I laid out on my number line here?

OK, so I'm going to start with 0. So 0, I had one, two 0's. So what I'm going to do is stack two dots like so. OK, so this represents two people had zero siblings. OK, so next I'm going to go to 1.

So 1, 2. OK, so I had two 1's. OK, now what I want to make sure I do, when I do my next one here, is that I maintain the same spacing between dots, and I make my dots about the same size so that-- since 0 had a frequency of two and 1 had a frequency of two, the two stacks of dots should be the same height. OK, now let's go to 2.

So we have one, two, three, four, five 2's. So I'm going to go up. I need to make five stacked dots. OK. That'll be like so. Again, making your dots about the same size, and then keeping the spacing consistent between your dots.

All right, 3. One, two. OK, so that's 3.

So two people had three siblings. OK, on to 4. One, two.

OK, 5. We had looks like just one. Again, notice all of these dots are right in a row.

OK, 6. Now, I didn't have anybody who had 6 siblings, so I'm going to just leave that blank. And then my last data value is a 7 there, so I'm going to make one dot here at 7.

OK, so again where a gap indicates that nobody had that value of whatever you're measuring. So in this case, siblings. All right, so this gives you a pretty nice way of displaying the data.

We can obviously see clearly here that most people had two siblings. 0 1, 3, and 4-- they were all very similar. Only two people had each of those numbers of siblings. 7 is out here. That's certainly the maximum.

And it was a little bit above because nobody even had six siblings. So there's a lot of different information you can gain from making a dot plot. And again, this was this was the main idea behind making it.

So again, the first thing you do is you make your number line. Make sure when you're making your number line, you don't skip any values. A lot of times what people do is, because they didn't have a 6, they'll leave 6 off and jumped from 5 to 7.

OK, make sure you don't do that. Gaps are very meaningful when making a dotplot so make sure that you get a good consistent scale before you start. So that has been your tutorial on dotplot. Thanks for watching.