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I want to talk briefly about Crosstabs. Crosstabs are a useful way to look at relationships among categorical– in other words nominal or ordinal– variables. So let’s go ahead and take a look. In this case, we might look at the overlap or relationship between two different coffee preferences. For instance, we might ask people whether they prefer decaf or full caff. And we might also ask people whether they prefer sugar or not. These are both categorical variables. In other words, they’re nominal variables. And so we can look at the Crosstabs. We could make a 2 by 2 grid representing all four permutations of these two variables.
Then within that, we could put the number of people who identify in each of those four boxes. This lets us to briefly see and understand the relationship between these two variables. Now in Excel, you could make this– it would be a pivot table, which we will get to do in the labs. But this is a useful way to illustrate these relationships. We could also begin to draw other kinds of conclusions. For instance, we could look at, among the decaf drinkers, so just the top row, 20 prefer no sugar, and 10 prefer sugar. Or in other words, a third of them are going to add sugar.
However, if we go down to the bottom row, the people who prefer full caffeine, in fact, the relationship is quite the opposite. The majority now prefer sugar. So we can begin to tell stories this way about the relationships between our categorical variables, which is very important, because we often have many categories in our data.

Lesson 3: Proportions

In this lesson, we’ll look at the basics of using proportions and percentages to summarize different aspects of data with two or more variables. We’ll also add another powerful Excel tool to our toolbelts: crosstabs/pivot tables.

Lab: Proportions

Hopefully you’re not getting tired of coffee talk yet, because in this lab, we’ll create a crosstab for two of the categorical variables in the coffee data set we’ve been using. Using pivot tables, we’ll organize these categories into raw counts and proportions in a couple different ways.

The lab instructions can be downloaded as a PDF file here.

The data set for this lab can be viewed here. From the link, copy and paste all the data into a new worksheet in Excel Online.

(Note: This lab uses the same data set you used in the labs for the previous module.)

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Essential Mathematics for Data Analysis in Microsoft Excel

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