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Winthrop Poll
Winthrop Poll
10 Dinkins Hall
Rock Hill, SC 29733, USA

Methodology Statement

Survey Methodology

December 2015 Winthrop Poll of Likely Voters in the SC Republican Presidential Primary

The December 2015 Winthrop Poll interviewed 828 Likely Voters in the 2016 SC Republican Presidential Primary (aged 18 and older, registered to vote, screened for likelihood of voting in SC Republican Presidential Primary). Results which use all respondents have a margin of error of approximately +/- 3.4% at the 95% confidence level. Results that use less than the full sample will naturally have a higher margin of error.  Results for those who Approve of the Tea Party have a margin of error of approximately +/- 5% at the 95% confidence level. Results for Evangelicals have a margin of error of approximately +/- 4.5% at the 95% confidence level. Results for those who Support a Database of Muslims have a margin of error of approximately +/- 5% at the 95% confidence level. Results for those who describe themselves as Angry at Government have a margin of error of approximately +/- 5.8% at the 95% confidence level.  Results for Trump Supporters have a margin of error of approximately +/- 7% at the 95% confidence level. Margins of error are based on weighted sample size.

The survey was in the field from 11/30-12/7, 2015. 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 survey used (1) Registration Based Sample (RBS) of previous Republican Primary voters,(2) Random Digit Dialing (RDD), and (3) 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 simply because their number is not listed in the previous voter sample.  MOST IMPORTANTLY, RDD and Wireless are necessary to capture any voters who are likely to vote in this contest, but did not vote in previous primaries (e.g. new to SC, newly registered voters, more interest in this contest, etc.) Both the RDD sample and the wireless sample were purchased from Survey Sampling International (SSI). RBS sample was purchased from Aristotle/Voter Lists Online.

Phone numbers selected for the survey were re-dialed five or more times in an attempt to reach a respondent.  Once a household was reached, we also employed procedures to randomize within households for RDD sample.  Numbers reached via RBS asked for specific randomly selected voters. Surveys were conducted in English.  

Additionally, we screen for voter registration status, screen for certainty of up-to-date registration status, screen OUT  Democrats and Democratic-Leaning Independents,  screen for likelihood of voting, and weight by sex, age, and race.

About our screen: Some surveys take respondents who say they will "Definitely" or "Probably" vote in primary. Our screen is a bit stricter; after two registration screens (moot for those we call via RBS), we ask them to rate their probability of voting on a scale of 1 to 10 and only take 7-10 (8-10 if polled within a month of the election).

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.