Consider the sample in the data file agstrat.xlsx (on the course website) with the four census regions (in the column labelled region) in the textbook Example 3.2. Using these census regions, estimate the population mean y using post and approximate the variance using (y post) and then approximate the 95% confidence interval for the population mean doing all these calculations with the package survey in R assuming a simple random sample. Then do all the calculations again with survey in R assuming a stratified random sample for these census regions. Compare and discuss your answers obtained by poststratification and stratification.