A description of RDD and GENESYS-ID+
(The non-productive number purge)
RDD Sample Methodology. The RDD sample that was utilized for this project can be best characterized as a single stage epsem sample of all residential telephone numbers (including listed, unlisted and non-published numbers) in the defined sample frame. The following paragraphs detail the underlying methodology.
The system utilizes a database consisting of all residential telephone exchanges, working bank information, and various geographic service parameters such as state, county, Primary Zip code, etc. In addition, the database provides working bank information at the two-digit level - each of the 100 banks ( i.e., first two digits of the four-digit suffix) in each exchange is defined as "working" if it contains one or more listed telephone households. On a National basis, this definition covers an estimated 96.4% of all residential telephone numbers and 99.96% of listed residential numbers. This database is updated on a quarterly basis.
The sample frame consists of the set of all telephone exchanges which meet the geographic criteria. This geographic definition is made using one or more of the geographic codes included in the database. Following specification of the geographic area, the system selects all exchanges and associated working banks which meet those criteria.
Based on the sample frame defined above, the system computes an interval such that the number of intervals is equivalent to the desired number of sample pieces. The interval is computed by dividing the total possible telephone numbers in the sample frame (i.e., # of working banks X 100) by the number of RDD sample pieces required. Within each interval a single random number is generated between 1 and the interval size; the corresponding phone number within the interval is identified and written to an output file.
The result, is that every potential telephone number within the defined sample frame has a known and equal probability of selection.
GENESYS-ID+. This process is designed to purge a percentage (approximately 75%) of two types of telephone numbers from the sample--business and non-productive numbers. Since this process is completed after the sample is generated, the statistical integrity of the sample is maintained.
To purge the business numbers, a database comprised of non-residential yellow page businesses is utilized. The distinction of non-residential is important because over one million households nationwide use their residential phone number for business purposes as well. The generated sample is compared to this database, and any matching telephone numbers are purged from the sample.
The remaining numbers that are not purged from the sample are then examined to determine if they are non-productive.