Vice Dean Michael Dorf's Columns About the Survey on FindLaw.com
"Americans' Knowledge of the U.S.
A Columbia Law Survey
-CARAVAN Telephone Sampling Methodology
-Reliability of Survey Percentages
-Sampling Tolerances When Comparing Two Samples
-Introduction to Detailed Tabulations
-Detailed Tabulations (requires Adobe Acrobat)
CARAVAN TELEPHONE SAMPLING
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