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In this course, author Barton Poulson takes a practical, visual, and non-mathematical approach to the basics of statistical concepts and data analysis in SPSS, the statistical package for business, government, research, and academic organization. From importing spreadsheets to creating regression models to exporting presentation graphics, this course covers all the basics, with an emphasis on clarity, interpretation, communicability, and application.
Once your data is in SPSS, one of the best ways to understand it is with charts, and most basic kind of chart is a bar chart. This simply indicates how many people or cases fall into each particular category. One of the great developments in SPSS a few versions ago was something called the Chart Builder, which is a unified interface for nearly every kind of chart that SPSS can make. Now I'm going to show you how to use the Chart Builder to create a simple bar chart to show frequencies, or how common particular categories are.
I'm using a data set right here, this is called Movies.sav. This is a data set that I and my research colleagues put together that included the top grossing movies from each of several years, as well as movies that won awards in several different categories, from the Academy Awards. What I'm going to do right here is I'm simply going to find out how many movies in this are in each different genre. Now this is a text variable, and we're going to make a bar chart to show the categories. I simply come up to Graphs, to Chart Builder, and then by default right here it offers bar charts, that's the first one, and I just want the simplest kind possible.
As a general rule, data graphics are designed to communicate, and they need to communicate clearly, and you want to use this simplest possible kind of chart that you can make, and a bar chart is a great one. And all I'm going to do is I'm going to come over to Genre. Please note it's got the three little circles that indicates its a nominal variable, and the A says that it's a text variable, as opposed to the year it released, which is also being treated as a categorical variable but it's got a number underneath it. So I'm going to just take this out of the variable list and I'm going to drag it into the canvas to right here under X axis.
One of the nice things is that the canvas automatically changes the Y axis on the side to read Count because that's the most common thing I would want do with a bar chart. Now I have lots of options here. One thing I can do, for instance, is I can just simply use the gallery to get lots of different kinds of charts. I'm using the basic one. Now if you can't find what you're looking for in the gallery, you can actually create a chart out of basic elements. It's a lot of work and we're not going to cover that one. There may be situations you want to be able to stick an identifier on a particular data point, and you can do that here. Or you can add titles and notes.
So for instance, I'm going to put Title 1, "Frequency of Movie Genres in the Dataset." Easy enough, and I press Apply. I can make other categories and other titles as well, but I'm not going to worry about those right now. All I'm going to do now is come over and press OK, and when I do to that, I get a large amount of output here that is the written record of a procedure that I just performed.
I get this that says GGraph-- that's the kind of graph we're making--the Source, the data set, and then here's the graph itself. And this shows, for instance, in this data set that that is based on top grossing movies and award winners, the dramas are more common than anything else, and that thrillers are the least common, most of this because a lot of these are drawn on award winners and thrillers win those less frequently than others. Now what I want to show you is there are ways to clean up these charts and to modify them to make them work little better. Aside from the simple fact that I think this is an ugly color, there are a lot of things that can be done to make this more communicative.
To enter the chart in SPSS, all you've got to do is you come over it and you double-click. And this brings up the Chart Editor window. When you're doing your charts, you want to look at the order that the bars appear in. Now by default, SPSS puts them in alphabetical order, and there may be situations in which that's appropriate. However, it's usually easier to read charts if you sort the data by their values. In this case, I'd like to have the most common to the least common, and what I'm going to do here as I just click on the bars and I come over here to the Properties window and it says Categories, Sort By, at the moment it says Custom. I just want to put it as Statistic, and I'm going to make it Descending, and I press Apply.
And now I see it goes from Drama, the most common, to Documentary, to Action, to Foreign, to Comedy, to Animated, to Thriller. If I want to change the colors of these-- these are still selected--I come over to Fill and Border, and I can change into a color that I find a little nicer. Now personally, I like to use light colors because I feel that it's easier to see them, but it does not dominate the vision. And so I've changed these to blue with a blue border as well. Also if you want to make these ones down here larger, these words, you can simply click on them and come over to Text Size.
The preferred size is 8 point, which is really small, especially since most of the time these charts are going to be used in presentations, like in PowerPoint, where people are going to be sitting 20, 30, 40 feet away. So you can change these to be 12 point, for instance. Now what's happened is that SPSS has automatically changed them to a staggered layout. That's because they'd run over to each other were documenters much longer, and animated and much longer. One way to deal with this, and something that I do frequently, is when I have a chart like this, you can actually come up to the button that says Transpose the chart coordinate system.
If I click on that, it switches the chart so that the labels are on the left and then the bars go off to the right. Now one thing that's happened to this is that the most common one is down by the bottom where the axis is. That's not helpful in this kind of chart, and so I'm going to click on the Categories, I'm going to click on the bars, go back to Categories, and instead of doing them Descending, I'll do them Ascending. And this puts the most common category on the top and the least common on the bottom. Also it may be that I don't really feel like I need this word Genre here in the title.
What I can do is I can click on that and I can come over to Labels & Ticks in the Property window and simply uncheck Display the axis title. I click that, and the way it works in SPSS as almost any time you're going to do anything, you then have to apply it. I apply it, and that disappears, and I find this to be a much cleaner chart. And as a bar chart, it displays very well. The prevalence of each category, it puts them into a logical order from most common to least common, the labels are large enough that I can read them, and I've been able to work on this very nicely.
Now once you've set up a chart in a way that you've modified it a fair amount, if you want to, you can come back to the Chart Editor and click on File and actually save this as a chart template. And it gives you the option of saving all of your settings, except I don't want to save all of the Text Content, so I will undo that, and I can say Continue. And I can simply save it as a Bar Chart Template Transposed, or whatever you think might be useful for you to find that template again in the future. I'll click Save, and now I can apply that template on other charts if I want to.
But this is the most basic kind, and truthfully, one of the most informative kinds of charts, the bar chart, a simple bar chart, two-dimensional, that communicates the frequency of categories in a categorical variable.
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