Winthrop University: Winthrop Poll - Current Poll Methodology
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Winthrop Poll
10 Dinkins Hall
Rock Hill, SC 29733, USA

Methodology Statement


Survey Methodology

April 2019 Winthrop Poll 

For this latest Winthrop Poll, callers surveyed 942 adult residents in South Carolina by landline and cell phone March 30 through April 13. The prolonged dates are due to the fact that the calling center was converting to a new Computer-Assisted Telephone Interviewing (CATI) system and for work on survey contracts. All respondents have a margin of error of approximately +/- 3.2% at the 95% confidence level. Any subset will have a larger margin of error. Margins of error are based on unweighted sample size and account for design effects.

Phone calls were made during weekday evenings, all day Saturday, and Sunday afternoon and evening. Weekday daytime calls are not made to avoid oversampling those who are more likely to be at home during the day (e.g. retirees, stay-at-home-parents, etc.). Conducting weekend calls is important to avoid systematically excluding certain populations (such as those who may work 2nd or 3rd shift during the week). This poll was in the field from November 10 - 20 and November 26 - December 2, 2018. The prolonged, and odd, dates are due to the fact that the Center was converting from regular phonelines to VOIP and only half of our phone were working for the first leg of the survey. We also took a break over the Thanksgiving holiday.

The survey used (1) Random Digit Dialing (RDD) and (2) Wireless phone number sampling. Both RDD and wireless samples are crucial to ensure no adult in the geographical area of interest is systematically excluded from the sample.  All samples were purchased from Survey Sampling International (SSI). 

Data are weighted based on age, sex, and race using Census Bureau data.

Phone numbers selected for the survey were re-dialed up to 5 times in an attempt to reach a respondent.  Once a household was reached, we also employed procedures to randomize within households for RDD sample.  Surveys were conducted in English.  

Computerized autodialers were not used in order to ensure the survey of wireless phones complied with the Telephone Consumers Protection Act and all FCC rules regarding contacting wireless telephones.  76% of the completions came from the wireless sample.

The Winthrop Poll is paid for by Winthrop University.

Additional Explanation of RDD Methodology : (with descriptions taken from SSI website)

Samples are generated using a database of "working blocks." A block (also known as a 100-bank or a bank) is a set of 100 contiguous numbers identified by the first two digits of the last four digits of a telephone number. For example, in the telephone number 203-567-7200, "72" is the block. A block is termed to be working if some specified number of listed telephone numbers are found in that block.

Samples of random numbers distributed across all eligible blocks in proportion to their density of listed telephone households are selected. All blocks within a county are organized in ascending order by area code, exchange, and block number. Once the quota has been allocated to all counties in the frame, a sampling interval is calculated by summing the number of listed residential numbers in eligible blocks within the county and dividing that sum by the number of sampling points assigned to the county. From a random start between zero and the sampling interval, blocks are systematically selected in proportion to their density of listed households. Once a block has been selected, a two-digit number is systematically selected in the range 00-99 and is appended to the exchange and block to form a 10-digit telephone number.

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Last Updated: 7/3/19