HCD 300 - Homework 7
The average BMI for a sample of 10 students is 16.1, with a standard deviation of 1.4. What is the 90% confidence interval for the BMI of all students?
- (15.29, 16.91)
The average BMI for a sample of 10 preschoolers is 16.3, with a standard deviation of 1.4. What is the 90% confidence interval for the BMI of all preschoolers? (round to two decimal places)
- (15.49, 17.11)
If in a sample of 355 adult males, we have a mean total cholesterol level of 185 mg, with s = 16. What is the 99% confidence interval for mean total cholesterol level of all males?
- (182.81, 187.19)
If in a sample of 355 adult females, we have a mean total cholesterol level of 185 mg, with s = 16. What is the 95% confidence interval for mean total cholesterol level of all females?
- (183.34, 186.66)
In a randomly selected sample of 500 Phoenix residents, 445 supported mandatory sick leave for food handlers. Legislators want to be very confident that voters will support this issue before drafting a bill. What is the 99% confidence interval for the percentage of Phoenix residents who support mandatory sick leave for food handlers?
- (85.4%, 92.6%)
What is the constant used to calculate the 90% confidence interval of the mean when n=50?
- 1.645
If df=22, what constant do we use to calculate the 90% confidence interval of the mean?
- 1.717
If n=15, what constant do we use to calculate the 95% confidence interval of the mean?
- 2.145
The t score constant used in calculating the 95% confidence interval with df=5:
- 2.571
The constant used in calculating the 99% confidence interval in the proportion formula is:
- 2.576
If n=20, what constant do we use to calculate the 99% confidence interval of the mean?
- 2.861
When calculating the 99% confidence interval of the mean for a sample of 15 patients, what constant is used in the formula?
- 2.977
For a sample with df = 5, what is the t-score constant to calculate a confidence level of 95%?
- 4.032
For a sample with df = 5, what is the t-score constant to calculate a confidence level of 99%?
- 4.032
How does the confidence interval relate to the significance level?
- Confidence intervals are a corollary of significance levels. For example, if alpha=.05, then you can calculate the 95% CI
What CI formula would you use for a sample size of 100 subjects?
- Interval/Ratio formula using the Z score
What CI formula would you use for a sample size of 36 subjects?
- Interval/Ratio formula using the z score
When calculating confidence intervals in this class the product of a constant times a margin of error is added and subtracted to what value to obtain the CI range?
- Mean
What affects the width of a confidence interval? (choose one or more)
- Sample size - Variation within the population - Our desired confidence level
What happens to the confidence interval if we increase our sample size?
- The confidence interval decreases
What happens to the confidence interval if we decrease our sample size?
- The confidence interval increases
Which of the following is/are true about the Excel function = CONFIDENCE.NORM
- This is the appropriate function to use if the sample size is greater than 30 - This function uses the normal distribution (table B.1)
Why do we need confidence intervals?
- To give insight about the magnitude of the effect and accurately state a range of a population parameter
Researchers find that the 90% confidence interval for men's systolic blood pressure is (126.8, 129.9). How would you interpret this?
- We are 90% confident that the true mean for men's systolic blood pressure is between 126.8 and 129.9.
How do you interpret the confidence interval for a final exam score at a significance level of 5% that is written (71.65, 77.26)?
- We are 95% confident that the true mean final exam score is between 71.65% and 77.26%
Researchers find that the 95% confidence interval for women's systolic blood pressure is (126.67, 127.93). How do you interpret this finding?
- We are 95% confident that the true mean for women's systolic blood pressure is between 126.67 and 127.93.
When would you use the confidence interval formula for a proportion? (choose one or more)
- You have summary information as a percentage or survey sample data - you do not know the st dev
Which of the following is/are true about confidence intervals (choose one or more)
- confidence interval of the mean = mean +/- a margin of error - confidence intervals are abbreviated CI - knowing the range of a parameter is more accurate than a point estimate
As you increase your confidence level, what happens to the width of the confidence interval?
- it gets wider
If you use the Excel Data Analysis Tools to calculate the descriptive statistics and check the box "confidence level for mean" what do you do with this number to obtain the confidence interval? (choose one or more)
- use this value to calculate the lower and upper bound of the interval - add and subtract this value to the mean
Why do we need confidence intervals? (choose one or more)
-To give insight about the magnitude of the effect - To accurately state a range of a population parameter - To express statistical uncertainty
What does a confidence interval tell you?
The best estimate of the range of a population value
