An eighth-grade student in Canada was concerned that air dryers in public restrooms were too loud, especially when measured at the height of children’s ears. Her results were eventually published in Paediatrics & Child Health (Keegan, 2019). The results, in A-weighted decibels (dBA), from 22 different makes and models of air dryers taken at a height of 30 cm (Keegan’s ear height at the start of the study), can be found in the file AirDryers. Look at a graph of the data using the Theory-Based Inference applet. 

a. What is an obvious interesting characteristic of the distribution? Explain why using a mixture of older-style air dryers and newer more intense air dryers could lead to such results. 

b. What is the mean dBA value for the dataset? 

c. Assuming the selection of air dryers is representative of all air dryers found in restrooms, find a 95% confidence interval for the population mean dBA for all air dryers. 

d. What proportion of all the dBA measurements from the data lie inside your 95% confidence interval? Explain why that proportion does or does not make sense.