The bigcity data frame has 49 rows and 2 columns.
The city data frame has 10 rows and 2 columns.
The measurements are the
population (in 1000's) of 49 U.S. cities in 1920 and 1930.  The 49 cities are 
a random sample taken from the 196 largest cities in 1920.  The city data 
frame consists of the first 10 observations in bigcity.
bigcityThis data frame contains the following columns:
uThe 1920 population.
xThe 1930 population.
Davison, A.C. and Hinkley, D.V. (1997) Bootstrap Methods and Their Application. Cambridge University Press.