ST 555 -- Summer 2013

  Homework #3 -- Due TUESDAY, 11 June 2013

  In the file crcell.dat are ratings of Cell Phone Service Providers 
  from Consumer Reports.  The ratings are given for 23 cities for five
  service providers; note that some providers do not service all cities.
  
  The first 3 records form the header (so use FIRSTOBS=4 in your INFILE
  statement).  Each city forms a collection of 15 records, with provider
  name on one record, its rating on the next, and then a blank line.
  If a carrier/service provider does not service a particular city, then
  its rating will be 'NA.'  Also note that some of the records are 
  shorter than others, as service providers and city names differ in 
  length -- so include 'PAD' in your INFILE statement.
  
  1) Read in these data to form a SAS dataset with 23*5=115 observations
  with (at least) variables CITY, CARRIER, and RATING.

  2) With a PROC FREQ, check to see whether you have one rating from 
  each carrier for each city.  Strip out unnecessary information.

  3) Determine the number of cities served by each carrier.
 
  4) Determine the number of carriers in each city.

  5) Find the mean rating (and its standard error) for each carrier.
                             
       FOR ALL EXERCISES: Hand in
        (1)  Your program
            * With as many comments as you have toes! *
        (2)  Your output
        (3)  The answers to the questions asked.