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Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc.
Hypothesis
Testing –
Examples and
Case Studies
Chapter 23
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 2
23.1 How Hypothesis Tests
Are Reported in the News
1. Determine the null hypothesis and the
alternative hypothesis.
2. Collect and summarize the data into a
test statistic.
3. Use the test statistic to determine the p-value.
4. The result is statistically significant if the
p-value is less than or equal to the level of
significance.
Often media only presents results of step 4.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 3
23.2 Testing Hypotheses About
Proportions and Means
If the null and alternative hypotheses are
expressed in terms of a population proportion,
mean, or difference between two means and if
the sample sizes are large …
… the test statistic is simply the corresponding
standardized score computed assuming the null
hypothesis is true; and the p-value is found from
a table of percentiles for standardized scores.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 4
Example 2: Weight Loss for Diet vs Exercise
Diet Only:
sample mean = 5.9 kg
sample standard deviation = 4.1 kg
sample size = n = 42
standard error = SEM1 = 4.1/ √42 = 0.633
Exercise Only:
sample mean = 4.1 kg
sample standard deviation = 3.7 kg
sample size = n = 47
standard error = SEM2 = 3.7/ √47 = 0.540
Did dieters lose more fat than the exercisers?
measure of variability = [(0.633)2 + (0.540)2] = 0.83
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 5
Example 2: Weight Loss for Diet vs Exercise
The sample mean difference = 5.9 – 4.1 = 1.8 kg
and the standard error of the difference is 0.83.
Step 1. Determine the null and alternative hypotheses.
Null hypothesis: No difference in average fat lost in population
for two methods. Population mean difference is zero.
Alternative hypothesis: There is a difference in average fat lost in
population for two methods. Population mean difference is not zero.
Step 2. Collect and summarize data into a test statistic.
So the test statistic: z = 1.8 – 0 = 2.17
0.83
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 6
Example 2: Weight Loss for Diet vs Exercise
Step 3. Determine the p-value.
Recall the alternative hypothesis was two-sided.
p-value = 2 × [proportion of bell-shaped curve above 2.17]
Table 8.1 => proportion is about 2 × 0.015 = 0.03.
Step 4. Make a decision.
The p-value of 0.03 is less than or equal to 0.05, so …
• If really no difference between dieting and exercise as fat
loss methods, would see such an extreme result only 3% of
the time, or 3 times out of 100.
• Prefer to believe truth does not lie with null hypothesis.
We conclude that there is a statistically significant
difference between average fat loss for the two methods.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 7
Example 3: Public Opinion About President
On May 16, 1994, Newsweek reported the results of a
public opinion poll that asked: “From everything you
know about Bill Clinton, does he have the honesty and
integrity you expect in a president?” (p. 23).
Poll surveyed 518 adults and 233, or 0.45 of them
(clearly less than half), answered yes.
Could Clinton’s adversaries conclude from this that
only a minority (less than half) of the population of
Americans thought Clinton had the honesty and
integrity to be president?
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 8
Example 3: Public Opinion About President
Step 1. Determine the null and alternative hypotheses.
Null hypothesis: There is no clear winning opinion on this issue;
the proportions who would answer yes or no are each 0.50.
Alternative hypothesis: Fewer than 0.50, or 50%, of the population
would answer yes to this question. The majority do not think Clinton
has the honesty and integrity to be president.
Step 2. Collect and summarize data into a test statistic.
Sample proportion is: 233/518 = 0.45.
The standard deviation = (0.50) × (1 – 0.50) = 0.022.
518
Test statistic: z = (0.45 – 0.50)/0.022 = –2.27
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 9
Example 3: Public Opinion About President
Step 3. Determine the p-value.
Recall the alternative hypothesis was one-sided.
p-value = proportion of bell-shaped curve below –2.27
Exact p-value = 0.0116.
Step 4. Make a decision.
The p-value of 0.0116 is less than 0.05, so we conclude
that the proportion of American adults in 1994 who
believed Bill Clinton had the honesty and integrity they
expected in a president was significantly less than a
majority.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 10
23.3 Revisiting Case Studies:
How Journals Present Tests
Whereas newspapers and magazines
tend to simply report the decision from
hypothesis testing, journals tend to
report p-values as well.
This allows you to make your own
decision, based on the severity of a
type 1 error and the magnitude of
the p-value.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 11
Case Study 5.1: Quitting Smoking with
Nicotine Patches
Compared the smoking cessation rates for smokers
randomly assigned to use a nicotine patch versus a
placebo patch.
Null hypothesis: The proportion of smokers in the
population who would quit smoking using a nicotine
patch and a placebo patch are the same.
Alternative hypothesis: The proportion of smokers
in the population who would quit smoking using a
nicotine patch is higher than the proportion who
would quit using a placebo patch.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 12
Case Study 5.1: Quitting Smoking with
Nicotine Patches
Higher smoking cessation rates were observed in the active
nicotine patch group at 8 weeks (46.7% vs 20%) (P < .001)
and at 1 year (27.5% vs 14.2%) (P = .011).
(Hurt et al., 1994, p. 595)
Conclusion: p-values are quite small: less than 0.001
for difference after 8 weeks and equal to 0.011 for
difference after a year. Therefore, rates of quitting are
significantly higher using a nicotine patch than using
a placebo patch after 8 weeks and after 1 year.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 13
Case Study 6.4: Smoking During
Pregnancy and Child’s IQ
Study investigated impact of maternal smoking on
subsequent IQ of child at ages 1, 2, 3, and 4 years of age.
Null hypothesis: Mean IQ scores for children whose mothers
smoke 10 or more cigarettes a day during pregnancy are same
as mean for those whose mothers do not smoke, in populations
similar to one from which this sample was drawn.
Alternative hypothesis: Mean IQ scores for children whose
mothers smoke 10 or more cigarettes a day during pregnancy
are not the same as mean for those whose mothers do not
smoke, in populations similar to one from which this sample
was drawn.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 14
Case Study 6.4: Smoking During
Pregnancy and Child’s IQ
Children born to women who smoked 10+ cigarettes per day
during pregnancy had developmental quotients at 12 and 24
months of age that were 6.97 points lower (averaged across
these two time points) than children born to women who did
not smoke during pregnancy (95% CI: 1.62,12.31, P = .01);
at 36 and 48 months they were 9.44 points lower (95% CI:
4.52, 14.35, P = .0002). (Olds et al., 1994, p. 223)
Researchers conducted two-tailed tests for possibility the
mean IQ score could actually be higher for those whose
mothers smoke. The CI provides evidence of the direction in
which the difference falls. The p-value simply tells us there
is a statistically significant difference.
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 15
For Those Who Like Formulas
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 16
For Those Who Like Formulas
Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 17
For Those Who Like Formulas

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STA10lecture21.pdf

  • 1. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. Hypothesis Testing – Examples and Case Studies Chapter 23
  • 2. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 2 23.1 How Hypothesis Tests Are Reported in the News 1. Determine the null hypothesis and the alternative hypothesis. 2. Collect and summarize the data into a test statistic. 3. Use the test statistic to determine the p-value. 4. The result is statistically significant if the p-value is less than or equal to the level of significance. Often media only presents results of step 4.
  • 3. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 3 23.2 Testing Hypotheses About Proportions and Means If the null and alternative hypotheses are expressed in terms of a population proportion, mean, or difference between two means and if the sample sizes are large … … the test statistic is simply the corresponding standardized score computed assuming the null hypothesis is true; and the p-value is found from a table of percentiles for standardized scores.
  • 4. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 4 Example 2: Weight Loss for Diet vs Exercise Diet Only: sample mean = 5.9 kg sample standard deviation = 4.1 kg sample size = n = 42 standard error = SEM1 = 4.1/ √42 = 0.633 Exercise Only: sample mean = 4.1 kg sample standard deviation = 3.7 kg sample size = n = 47 standard error = SEM2 = 3.7/ √47 = 0.540 Did dieters lose more fat than the exercisers? measure of variability = [(0.633)2 + (0.540)2] = 0.83
  • 5. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 5 Example 2: Weight Loss for Diet vs Exercise The sample mean difference = 5.9 – 4.1 = 1.8 kg and the standard error of the difference is 0.83. Step 1. Determine the null and alternative hypotheses. Null hypothesis: No difference in average fat lost in population for two methods. Population mean difference is zero. Alternative hypothesis: There is a difference in average fat lost in population for two methods. Population mean difference is not zero. Step 2. Collect and summarize data into a test statistic. So the test statistic: z = 1.8 – 0 = 2.17 0.83
  • 6. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 6 Example 2: Weight Loss for Diet vs Exercise Step 3. Determine the p-value. Recall the alternative hypothesis was two-sided. p-value = 2 × [proportion of bell-shaped curve above 2.17] Table 8.1 => proportion is about 2 × 0.015 = 0.03. Step 4. Make a decision. The p-value of 0.03 is less than or equal to 0.05, so … • If really no difference between dieting and exercise as fat loss methods, would see such an extreme result only 3% of the time, or 3 times out of 100. • Prefer to believe truth does not lie with null hypothesis. We conclude that there is a statistically significant difference between average fat loss for the two methods.
  • 7. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 7 Example 3: Public Opinion About President On May 16, 1994, Newsweek reported the results of a public opinion poll that asked: “From everything you know about Bill Clinton, does he have the honesty and integrity you expect in a president?” (p. 23). Poll surveyed 518 adults and 233, or 0.45 of them (clearly less than half), answered yes. Could Clinton’s adversaries conclude from this that only a minority (less than half) of the population of Americans thought Clinton had the honesty and integrity to be president?
  • 8. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 8 Example 3: Public Opinion About President Step 1. Determine the null and alternative hypotheses. Null hypothesis: There is no clear winning opinion on this issue; the proportions who would answer yes or no are each 0.50. Alternative hypothesis: Fewer than 0.50, or 50%, of the population would answer yes to this question. The majority do not think Clinton has the honesty and integrity to be president. Step 2. Collect and summarize data into a test statistic. Sample proportion is: 233/518 = 0.45. The standard deviation = (0.50) × (1 – 0.50) = 0.022. 518 Test statistic: z = (0.45 – 0.50)/0.022 = –2.27
  • 9. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 9 Example 3: Public Opinion About President Step 3. Determine the p-value. Recall the alternative hypothesis was one-sided. p-value = proportion of bell-shaped curve below –2.27 Exact p-value = 0.0116. Step 4. Make a decision. The p-value of 0.0116 is less than 0.05, so we conclude that the proportion of American adults in 1994 who believed Bill Clinton had the honesty and integrity they expected in a president was significantly less than a majority.
  • 10. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 10 23.3 Revisiting Case Studies: How Journals Present Tests Whereas newspapers and magazines tend to simply report the decision from hypothesis testing, journals tend to report p-values as well. This allows you to make your own decision, based on the severity of a type 1 error and the magnitude of the p-value.
  • 11. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 11 Case Study 5.1: Quitting Smoking with Nicotine Patches Compared the smoking cessation rates for smokers randomly assigned to use a nicotine patch versus a placebo patch. Null hypothesis: The proportion of smokers in the population who would quit smoking using a nicotine patch and a placebo patch are the same. Alternative hypothesis: The proportion of smokers in the population who would quit smoking using a nicotine patch is higher than the proportion who would quit using a placebo patch.
  • 12. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 12 Case Study 5.1: Quitting Smoking with Nicotine Patches Higher smoking cessation rates were observed in the active nicotine patch group at 8 weeks (46.7% vs 20%) (P < .001) and at 1 year (27.5% vs 14.2%) (P = .011). (Hurt et al., 1994, p. 595) Conclusion: p-values are quite small: less than 0.001 for difference after 8 weeks and equal to 0.011 for difference after a year. Therefore, rates of quitting are significantly higher using a nicotine patch than using a placebo patch after 8 weeks and after 1 year.
  • 13. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 13 Case Study 6.4: Smoking During Pregnancy and Child’s IQ Study investigated impact of maternal smoking on subsequent IQ of child at ages 1, 2, 3, and 4 years of age. Null hypothesis: Mean IQ scores for children whose mothers smoke 10 or more cigarettes a day during pregnancy are same as mean for those whose mothers do not smoke, in populations similar to one from which this sample was drawn. Alternative hypothesis: Mean IQ scores for children whose mothers smoke 10 or more cigarettes a day during pregnancy are not the same as mean for those whose mothers do not smoke, in populations similar to one from which this sample was drawn.
  • 14. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 14 Case Study 6.4: Smoking During Pregnancy and Child’s IQ Children born to women who smoked 10+ cigarettes per day during pregnancy had developmental quotients at 12 and 24 months of age that were 6.97 points lower (averaged across these two time points) than children born to women who did not smoke during pregnancy (95% CI: 1.62,12.31, P = .01); at 36 and 48 months they were 9.44 points lower (95% CI: 4.52, 14.35, P = .0002). (Olds et al., 1994, p. 223) Researchers conducted two-tailed tests for possibility the mean IQ score could actually be higher for those whose mothers smoke. The CI provides evidence of the direction in which the difference falls. The p-value simply tells us there is a statistically significant difference.
  • 15. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 15 For Those Who Like Formulas
  • 16. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 16 For Those Who Like Formulas
  • 17. Copyright ©2005 Brooks/Cole, a division of Thomson Learning, Inc. 17 For Those Who Like Formulas