"PM" stands for Particulate Matter. "PM2.5" refers to fine inhalable particles in the air.

A random sample of households in China found that "each 1% decrease in yearly PM2.5 exposure is associated with a 0.536% (95% confidence interval: 0.378%, 1.033%) decrease in healthcare costs."

1. In the dataset used to produce these statistics, what is each case?

2. What are the two main variables?

3. Interpret the confidence interval.