Case Study 6.2: The Case of the Lost Mail
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Variables: 

  c62.surinfo.dat: 

      GROUP      grouping variable for post office zipcode  
      ID         post office zipcode  
      X          number of magazines sent to ID 
      STATE      state code of post office zipcode 
  
  c62.survey.dat: 
  
      ID               post office zipcode  
      Q1, Q2           Question 1, 2 responses (1 = yes, 0 = no)
      Q3A, Q3B, Q3C    Question 3A, 3B, 3C responses (percentage)
      Q4               Question 4 response (a,b,c, or d)
      
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