STAT 121: Writing Assignment 1 Confidence Intervals

Confidence Intervals (12 points)

Directions: Read the following article and answer each question completely but concisely. Be sure to save a copy of your work, and see the syllabus for submission details. (The spacing between the questions is not necessarily an indication of the expected response length.)

Journal March 26, 2010

Resting Heart Rates of American Adults

A normal resting heart rate for adults ranges from 60 to 100 beats a minute,” reports Dr. Edward Laskowski of the Mayo Clinic. Lower resting heart rates are generally associated with higher cardiovascular fitness. With the marked increase in obesity in America, there is rising concern that the average resting heart rate of American adults is trending towards the higher end of the accepted range. A recent study conducted by the Statistical Health Association of America validates this concern. Results were based on a sample of 1587 American adults (ages 18 and older). The mean resting heart rate from this sample was calculated at 87 beats per minute (bpm). The study concludes that, with 95% confidence, the true mean resting heart rate of American adults is in the interval (80, 94).

(1 point) What is the population that the confidence interval in the article is making an inference about? Be specific.

It is making an inference about all adults (ages 18 and older) in America.

(1 point) What is the parameter of interest for the confidence interval in context?

The parameter of interest is the true average resting heart rate of all American adults.

(2 points) Give the confidence interval as reported in the article. Is the reported interval in the form of an interval or is it in the form of estimate ± margin of error? If it is not in interval form, state it in interval form.

The confidence interval stated in the terms of the article is (80, 94). I believe that this confidence interval is given in interval form.

(3 points) What confidence level is associated with the given interval? Interpret this level of confidence.

The confidence level given with this interval is 95%. This means that the mean resting heart rate for all adults is somewhere between 80 and 94 beats per minute with 95% confidence. Another way to put it is 95% of all possible confidence intervals computed using the same procedure as used to obtain 80 and 94 will contain the value of μ.

(2 points) How was the sample collected? Does this allow us to infer things about the population? If the article does not state how it was collected, how SHOULD it have been collected?

This article does not specifically state how data was collected, but it should be collected as a simple random sample.

(3 points) Interpret your calculated interval in context. Make sure to include all three parts of a confidence interval interpretation.