The last section left us with the result where we saw that 10-year-old boys who live in areas with high levels of pollution had significantly lower lung volume, on average, as compared to the standard for all 10-year-old boys.
The question remains, however, of how much lower their lung volume is, on average. To answer that, we'll need to learn how to construct a Confidence Interval for a population mean, based on sample data.
We'll also have to deal with the fact that we don't know what the standard deviation is for a population when all we have is sample data. You'll learn about the t-distribution, which is very much like the z-distribution, and use t-values as you've used z-values in previous analysis.
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