Practice with Quantitative Skills
Professor Timothy Shortell
www.shortell.org/opp/crosstabs.html
crosstabulation
A two-way percentage table in which the variable believed to be the cause is given in the columns and the variable investigated as the effect is given in the rows. The values in the table are column percentages, the relative frequency of occurrence of the attribute in that column. If percentages are different across the columns, a relationship between the two variables is suggested.

Percentage Tables

To read a crosstabulation, follow these three steps: (1) determine if the result is statistically significant; if it is, then (2) interpret the pattern in the table; if not, stop; After you interpret the pattern (if the table is reliable), think about how the independent variable, in the columns, might be related to the dependent variable, in the rows.

Step 1.
Compare the value of "p" for Chi-square with the conventional criterion, 0.05, or 5%.

If you are challenged by decimal numbers, here is a simple technique for comparing values. Take the value of "p" and mulitply by 1,000. To get the result, move the decimal three places to the right, adding zeros if needed. For example, if p = 0.014, we would end up with 14. If p = 0.11, we would get 110. If p = 0.0057, we would get 5.7 . Next, do the same for the criterion, 0.05. This will always result in 50. Finally, compare the modified value of p with the modified criterion. For example, for p = 0.014, we have 14 compared to 50. Since 14 is less than 50, this result would be reliable. For p = 0.11, we have 110 compared to 50. Since 110 is greater than 50, this result is not reliable. For p = 0.0057, we have 5.7 compared to 50. Since 5.7 is less than 50, this result is reliable.

Step 2.
Compare the column percents across each row. If the percents are consistently different, the independent variable is related to the dependent variable.

Step 3.
Interpret the results from a social scientific perspective. Remember, the pattern describes general tendencies, or probabilities, rather than particular cases.

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