Which test to use?

1
Which test to use?

• X2 Goodness of Fit
• X2 Test for Homogeneity
• X2 Test for Independence

2
A brokerage firm wants to see whether the type of
account a customer has (Silver, Gold, Platinum)
affects the type of trades that a customer makes
(in person, by phone, or on the Internet). It
collects a random sample of trades made for its
customers over the past year and performs a test.
Chi-squared independence (one sample 2
variables)
3
A brokerage firm wants to see whether the type of
account a customer has (Silver, Gold, Platinum)
affects the type of trades that a customer makes
(in person, by phone, or on the Internet). It
collects a random sample of trades made for its
customers over the past year and performs a test.
That brokerage firm also wants to know if the
type of account affects the size of the account
(in dollars). It performs a test to see if the
mean size of the account is the same for the
three account types.
Chi-squared Goodness of Fit
4
The academic research office at a large community
college wants to see whether the distribution of
courses chosen (Humanities, Social Science, or
Science) is different for its residential and
nonresidential students. It assembles last
semesters data and performs a test.
Chi squared homogeneity (one variable 2 groups)
5
Is the quality of a car affected by what day it
was built? A car manufacturer examines a random
sample of the warranty claims filed over the past
two years to test whether defects are randomly
distributed across days of the work week.
Chi squared GOF (existing model)
6
A medical researcher wants to know if blood
cholesterol level is related to heart disease.
She examines a database of 10,000 patients,
testing whether the cholesterol level (in
milligrams) is related to whether a person has
heart disease or not.
Chi-squared independence (one sample 2
variables)
7
A student wants to find out whether political
leaning (liberal, moderate, or conservative) is
related to choice of major. He surveys 500
randomly chosen students and performs a test.
Chi-squared independence (one sample 2
variables)
8
Among randomly selected pets, 27 of the 188 dogs
and 18of the 167 cats had fleas. Does this
indicate a significant difference in rates of
flea problems for these two pets?
Difference of proportions (two samples)
9
A supermarket chain wants to know which of two
merchandise display methods is more effective.
They randomly assign 15 stores to use display
type A and 15 others to use display type B, then
collect data about the number of items sold at
each store.
Difference of means (two independent samples)
10
Are there more broken bones in summer or winter?
We get records about the number of fractures
treated in January and July at a random sample of
25 emergency rooms.
Mean of differences (matched pairs)