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HW#8: Chapter 2.5 page 142-148 Complete three questions on the last two slides
Do Now:
What percent of the women in our sample are frequent binge drinkers?
What percent of the men in our sample are frequent binge drinkers?
Describing relationships
Relationships among categorical data are described by calculating appropriate percents from the counts give
Comparing Percent and Joint Distribution
Why is percent more accurate than the joint distribution? To find joint distribution, you are
dividing each particular total you are looking at by the SAMPLE SIZE
To find the actual percentage of the particular group you are dividing the portion you want by the TOTAL OF THAT GROUP ONLY!
Conditional Distributions Conditional Distribution: condition on
the value of one variable and calculate the distribution of the other variable For the example we just did, we
calculated the percent for frequent binge drinkers only
The complete conditional distribution gives the proportions or percents for all possible values of the conditioning variable
Conditional Distribution: of binge drinking for women For women, the conditional distribution of
the binge-drinking variable in terms of percents is
Note that both Yes and No percentages are included (they should sum up to 100%)
Conditional Distribution: of binge drinking for men The same can be done for me
Comparing the Conditional Distributions… Reveals the nature of the association
between gender and frequent binge drinking
Bar graphs can also show this relationship between 2 categorical variables NOT single graphs like scatterplots and NO singe measure like correlation
Summary
A two-way table contains a great deal of information in compact form.
Making that information clear almost always requires finding percents.
You must decide which percents you need.
Using SPSS to compute joint, marginal, and conditional distributions
Homework:
1. Enrollment of recent high school graduates. The table below gives some census data concerning the enrollment status of recent high school graduates aged 16 to 24 years. The table entries are in thousands of students.
(a) How many male recent high school graduates aged 16 to 24 years were enrolled full-time in two-year colleges?
(b) Give the marginal distribution of gender for these students. Display the results graphically.
(c) What is the marginal distribution of status for these students? Display the results graphically.
Homework continued..
2. Condition on status. Refer to the previous exercise. Find the conditional distribution of gender for each status. Describe the distributions graphically and write a short summary comparing the major features of these distributions.
3. Condition on gender. Refer to the previous two exercises. Find the conditional distribution of status for each gender. Describe the distributions graphically and write a short summary comparing the major features of these distributions.
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