1. Statistics
Pooled Examples

2. Example #20 Page 510
A survey of 430 randomly chosen adults found that 21% of the 222 men and 18% of the 208 women purchased books online.
Is there evidence that men are more likely than women to make online purchases of books? Test an appropriate hypothesis and state your conclusion in context.

3. Example #20 Page 510 State the hypotheses
H0: The proportion of men who have purchased books on line is the same as the proportion of women who have purchased books online.
HA: The proportion of men who have purchased books on line is greater than the proportion of women who have purchased books online.

4. Example #20 Page 510 Part a continued. Randomization condition:
The men and women were chosen randomly.
10% condition:
222 and 208 are both less than 10% of all people.
Independent samples condition:
The groups were chosen independently.
Success/Failure condition:
All samples are greater than 10 so the samples are large enough.

5. Example #20 Page 510 Part a continued.
Since the conditions have been satisfied, we will model the sampling distribution of the difference in proportion with a Normal model with mean 0 and a standard deviation estimated by:

6. Example #20 Page 510 Part a continued.
The observed difference between the proportions is:
0.21 – 0.18 = 0.03
Since the P-value = is high, we fail to reject the null hypothesis. There is no evidence that the proportion of men who have purchased books online is greater than the proportion of women who have purchased books on line.

7. Example #20 Page 510 Part a continued.
We can construct a normal curve to show this.
P =
Z = 0.78

8. Example #20 Page 510
If your conclusion in fact proves to be wrong, did you make a Type I or Type II error?
If there is actually a difference between the proportions of men who have purchased books online and the proportion of women who have purchased books online, then we have committed a Type II error.