Health status. In the OECD 2020 How’s life? project, health status, one of the 11 dimensions determining quality of environment, depends on two data variables: air pollution and water quality. The 23 European countries in this study score an average of 13.64 micrograms per cubic meter on the air pollution with a standard deviation of 4.83 micrograms per cubic meter.

a) What assumptions and conditions must be checked before finding a confidence interval for the mean? How would you check them?

b) Find a 95% confidence interval for the mean value per European country.

c) Interpret this interval, and explain what 95% confidence means.

d) For all countries in the project, the average the air pollution is 12.25. Do you think the average the air pollution in Europe differs significantly from the overall average?

Explain.