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Winthrop Poll
10 Dinkins Hall
Rock Hill, SC 29733, USA
803/323-4962
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Methodology Statement

Survey Methodology

April 2016 Winthrop Poll Focusing on Race Relations in South Carolina

The April 2016 Winthrop Poll was unusual in several aspects.  First, this poll was in the field MUCH longer than a normal poll.  This poll was in the field from April 3 – April 24, 2016.  The reason is twofold: First, since this poll focused on race relations, we felt the need to get an oversample of African American residents in SC. The oversample contains more than twice the number of African American respondents as a typical Winthrop Poll. Second, this poll was much longer than a typical Winthrop Poll.  The mean completion time was 75% longer than normal. For these reasons, the poll needed to stay in the field longer than normal.  HOWEVER, this means no “hot button” questions, such as the ‘bathroom bill,’ the gas tax, ethics reform, and the like. We limited ourselves to core, established topics about which opinion was unlikely to shift dramatically during the time this poll was in the field.

The “main” poll is a General Population poll of 814 SC residents. Results which use All Respondents have a margin of error of approximately +/- 3.4% at the 95% confidence level. Results for Whites Only come exclusively from the “main” poll and have a margin of error of approximately +/- 4.1% at the 95% confidence level. Results for Blacks Only contain African American respondents from the “main” poll combined with those from the African American targeted “oversample” poll. Results for Blacks Only have a margin of error of approximately +/- 4.9% at the 95% confidence level. Without the oversample, the margin of error for African Americans would be +/- 7%.  Margins of error are based on weighted sample size.

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).

The “main” 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.  The “oversample” survey used (1) RDD which was targeted to Census areas in SC with populations that were 50% African American or higher and (2) Wireless phone numbers targeted by race of phone owner.  All samples were purchased from Survey Sampling International (SSI). 

Phone numbers selected for the survey were re-dialed up to seven 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.

The Winthrop Poll is paid for by Winthrop University with additional support from The West Forum on Politics and Policy at 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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