## Explain why the percentage of low-exposure people with wheeze symptoms is the same as the percentage of mail-return people with wheeze symptoms.

Case Study: Air Pollution and Respiratory Symptoms

Air pollution is a serious problem in many places. One form of air pollution that is suspected to cause respiratory illness is particulate matter (PM), which consists of tiny particles in the air. Particulate matter can come from many sources, most commonly ash from burning wood or from fossil fuel energy sources, but also from other courses such as tiny particles of rubber that wear off of automobile and truck tires.

The town of Libby, Montana was the focus of a 2004 study on the effect of PM on the respiratory health of children. Many houses in Libby are heated by wood stoves, which produce a lot of particulate pollution. The level of PM is greatest in the winter when more stoves are being used and declines as the weather becomes warmer. The study attempted to determine whether higher levels of PM affect the respiratory health of children. In one part o the study, schoolchildren were given a questionnaire to bring home to their parents. Among other things, the questionnaire asked whether the child had experienced symptoms of wheezing during the past 60 days. Most parents returned the questionnaire within a couple of weeks. Parents who did not respond promptly were sent another copy of the questionnaire through the mail. Many of these parents responded to this mailed version.

The data presents, for each day, the number of questionnaires that were returned by parents of children who wheezed, the number returned by those who did not wheeze, the average concentration of particulate matter in the atmosphere during the past 60 day (in units of micrograms per cubic meter) and whether the questionnaires were delivered in school or through the mail.

We will consider a PM level of 17 or more to be high exposure, and a PM level of less than 17 to be low exposure.

Answer the following questions. Unless noted, each question is worth 0.5 point:

How many people returned questionnaires?

Overall, what percentage of people wheezed?

How many people had high exposure to PM?

What percentage of the high-exposure people had wheeze symptoms?
How many people had low exposure to PM?

What percentage of the low-exposure people had wheeze symptoms?
What is the mean PM level?

What is the standard deviation of PM level?
Create a graph for one variable of your choice using technology. Explain why you chose this type of graph for this variable

Explain why the percentage of high-exposure people with wheeze symptoms is the same as the percentage of school-return people with wheeze symptoms.

Explain why the percentage of low-exposure people with wheeze symptoms is the same as the percentage of mail-return people with wheeze symptoms.

As the weather gets warmer, PM goes down because wood stoves are used less. Explain how this causes the response mode (school or mail) to be related to PM.

It is generally the case in epidemiological studies that people who have symptoms are often eager to participate, while people who are unaffected are less interested. Explain how this may cause the response mode (school or mail) to be related to the outcome.

Rather than send out questionnaires, the investigators could have telephoned a random sample of people over a period of days. Explain how this might have reduced the confounding.

Based on the results of this study, there was an intervention to phase out wood-burning stoves in the town. In 2012, a new study in the town found an average PM of 13.194 with a standard deviation of 2.13 and the new percent of people who reported wheezing was 6.7%.

Was the intervention effective? Write a paragraph explaining why or why not and support your answer with numerical evidence from the both original and new studies. (2 points)

Based on your analysis of the data, write a short (1 paragraph or more) article for a health blog whose audience is a group of your friends and neighbors. Give it a title. (1 point)

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