A Columbia Law Survey
May 2002

Conducted by       

Press Release

Fact Sheet

Vice Dean Michael Dorf's Columns About the Survey on

"Americans' Knowledge of the U.S. Constitution"
A Columbia Law Survey


 -Technical Information

 -CARAVAN Telephone Sampling Methodology

 -Reliability of Survey Percentages

 -Sampling Tolerances When Comparing Two Samples

 -Introduction to Detailed Tabulations

 -Significance Testing

 -Detailed Tabulations (requires Adobe Acrobat)






Opinion Research Corporation's national probability telephone sample is an efficient form of random-digit-dialing. The sample is designed to be a simple random sample of telephone households. Unlike published directories, Opinion Research Corporation's national probability telephone sample includes both unlisted numbers and numbers issued after publication of the directories. The following procedure was used to create the sample:

  • Opinion Research Corporation has an annual license for GENESYS, a custom RDD sample generation system developed by Marketing Systems Groups.

  • The methodology for generating random digit dialing (RDD) telephone samples in the GENESYS system provides for a single stage, EPSEM (Equal Probability of Selection Method) sample of residential telephone numbers. It is updated twice a year.

  • When a national probability sample is needed, a random selection is made from approximately 40,000 exchanges in two million working banks.

  • Each telephone number is transferred to a separate call record. The record shows the computer-generated telephone number to be called, as well as the county, state, MSA (if applicable), band and time zone into which the telephone number falls. Our computerized interviewing system (CATI) uses this information to keep track of regional quotas. The CATI interviewing program also keeps track of the disposition categories for each call attempt.

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