Hospital admissions for asthma in children younger than 15 years was studied in Scotland both before and after comprehensive smoke-free legislation was passed in March 2006. Monthly records were kept of the annualized percent change in asthma admissions. For the sample studied, before the legislation, admissions for asthma were increasing at a mean rate of 5.2% per year. The standard error for this estimate is 0.7% per year. After the legislation, admissions were decreasing at a mean rate of 18.2% per year, with a standard error of 1.79%. In both cases, the sample size is large enough to use a normal distribution. Note: the mean decrease of 18.2% means that we work with a value of -18.2%.


a) Find and interpret a 95% confidence interval for the mean annual percentage rate of change in childhood asthma hospital admissions in Scotland before the smoke-free legislation.

b) Find a 95% confidence interval for the same quantity after legislation.

c) Is this an experiment or an observational study?