Which of the following factors can make it difficult to make correct conclusions about the population based on confidence intervals?
a. Bias in the data collection or sampling process.
b. Confounding variables.
c. Sample sizes that are too small to detect true differences in the population.
d. All of the above.
Q. 2Suppose you are comparing the proportion of people who successfully stopped smoking on each of two different smoking cessation plans. You randomly assigned subjects to treatment, but you also collected data on each subject on a variety of measurement variables as well. How can this help you to verify that your randomization procedure worked?
Q. 3Journal articles often report means and standard deviations, and they also often report their results in the form (mean +/ standard deviation). Does this latter form represent a real confidence interval for the population mean? If yes, explain why. If not, tell what it does represent. (Assume the populations are bell-shaped.)
Q. 4To get the standard error for the difference in the means of two independent samples, you take the square root of the __________ of the squares of the individual standard errors.
Fill in the blank(s) with correct word
Q. 5The difference in the means of two independent samples has __________ variability than the mean of the differences in a matched-pairs sample. (Assume sample sizes are comparable and the values in the pairs are positively correlated.)
Fill in the blank(s) with correct word
Q. 6Suppose instead of comparing independent measurements taken from two groups, you used a matched-pairs experiment and one treatment is randomly assigned to each half of the pair. In this case, how should you compute the confidence interval for the difference?
a. Do it the same way you would do it for two independent groups. You'll just get more accurate results because they came from matched pairs.
b. Do a separate confidence interval for each half of the pair and subtract the confidence intervals to get a range of differences.
c. Compute the differences for each pair, treat them as a single data set, and use the formula for a confidence interval for one mean (the mean difference).
d. None of the above.
Quick Reply
