1. Discuss the difference between cross-sectional data and time series data. If we record the total number of cars sold in 2011 by each of 10 car salespeople, are the data cross-sectional or time series data? If we record the total number of cars sold by a particular car salesperson in each of the years 2007, 2008, 2009, 2010, and 2011, are the data cross-sectional or time series data?

1. Consider a medical study that is being performed to test the effect of smoking on lung cancer. Two groups of subjects are identified;