Question: Zar (1999) reports on the results of a study comparing concentrations of nitrogen oxides and hydrocarbons (in \(\mu \) g/m3) in an urban area that shall remain nameless (well, Zar forgot to name it, anyway). Both pollutants were measured on a representative sample of 11 days, with the following results:

(a) Does the mean difference in pollutant concentration seem large to you in practical terms? Explain briefly. [5 points]

(b) Set up a statistical model for this situation, being explicit about the population, sample and imaginary data sets, and use your model (including the usual inferential summary) to build a 95% confidence interval for the population mean difference in pollutants (what is the population here, precisely?). Is this difference large in statistical terms? Explain briefly. [10 points]