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# Crosstabs PowerPoint PPT Presentation

Crosstabs. How do we assess the relationship between two variables? (We’ll bring in more variables later.) Various ways, especially with interval-level data; one of the most common ways is with crosstabs. “Crosstab” is a contraction of “Cross Tabulation”

Crosstabs

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### Crosstabs

• How do we assess the relationship between two variables? (We’ll bring in more variables later.)

Various ways, especially with interval-level data;

one of the most common ways is with crosstabs.

• “Crosstab” is a contraction of “Cross Tabulation”

Also called a contingency table

• What is a (simple) crosstab?

A table based on two variables, where the cell

entries are the counts or percentages of cases

that fall in that row or column category.

So, also called a bivariate frequency table.

• WARNING:

• There’s going to be a lot coming at you (in class).

• It requires paying attention, thinking (wow!).

• But—it only involves percentages, so no complicated “statistics” (yet).

We begin with the observations (persons).

A file of about a thousand people would have data like this (except that Gender and Watching TV would be coded using numbers).

You would create the cross-tab (presumably using SPSS—these are real bears to do by hand).

### Are Women More Likely to Watch Than Men?

• You might want to ask the question: are women more likely to watch this particular tv program than men are?

• So, you display the data in a crosstab (in this case a 2x2 table).

• But how do you read it?

• Almost without exception, you want to look at percentages rather than numbers of cases.

• But, which way to percentage?

• Add to 100% within categories of the iv.

• In the way that makes sense for the question at hand. (Requires thinking.)

### We can % either way(by rows) (by columns)

• Note

I’ve percentaged the total row or col.

Not necessary, but often useful, and

it’s done automatically by SPSS.

I’ve used whole numbers. Nothing

accuracy level. Don’t overdo

accuracy.

• Which way is correct?

• Recall:

Dv is the one we’re trying to explain.

Iv is the one used to explain the dv.

The question we are asking is: are

women more likely to watch this

particular tv program than men are?

### Burning question

• Does it make any difference which variable makes up the rows, and which the columns?

• No. There’s no agreed-upon convention for whether the iv goes in the rows or columns (text notwithstanding). BUT

• If you switch row and column variables, then which percentages are right (for your question) will also change.

### More analytical matters. Illustration: Do different careers attract different partisans? (class survey)

• Are Democrats or Republicans more likely to go into:

• Law?

• Politics?

### Party ID * Career

Recode? Note small # of cases in some rows. Also, are Ind and Other different?

DKs? Delete or combine with other rows?

### More analytical matters (cont.)

• These are analytical matters.

Don’t make meaningless combinations

just because of small N’s.

Keep in/delete “don’t knows” depending

• Suppose we decide to keep DKs and combine the three smallest categories.

### Recoded

• Table is simpler, easier to read.

• More meaningful because it doesn’t make distinctions we aren’t really interested in.

### Final analytical matter

• How much of a difference is enough to be meaningful?

Important question

For now, see Weisberg et al. reading,

pp. 211-12.

You might want to look at this when

### Presentation matters

• DO NOT USE SPSS OUTPUT DIRECTLY

Reformat as necessary

Provide meaningful labels

Give it a title

Show n’s, %s, not cell counts

• Can be easily done in MSWord (maybe other ways as well)

Table 1. Career Interests by Party Identification

### Data Analysis #1Due one week from today (by ind’s, not pairs)

• Directions are on the syllabus

• Describe a hypothesis (NES or GSS).

Tell us why this hyp makes sense.

Thoughtfulness is rewarded. (Dem’s

more often voted for Gore is not that

thoughtful.)

• Discuss the opera’zation of your concepts.

Tell us how you operationalized your

variables, but also why.

• Generate an SPSS cross-tab to test your

hypothesis.

Percentage the table properly.

Presentation as noted earlier.

• Explain the table: is your hypothesis

supported?

(More than “yes” or “no” is required.)

Note possible alternative explanations.

• Usually ≤ 3 pp. (double-spaced) + table

Table should go on a separate page.

• Writing is important.

Use clear, straightforward prose (you

are not writing a novel).

Proper grammar; correct spelling,

punctuation, and capitalization; typo-

free