April 2015 Winthrop Poll of Likely GOP Presidential Primary Voters in SC
The April 2015 Winthrop Poll interviewed 956 Likely Voters in the 2016 SC GOP Presidential Primary (aged 18 and older, registered to vote, screened for likelihood of voting in SC GOP Presidential Primary). Results which use all respondents have a margin of error of approximately +/- 3.2% 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 only have a margin of error of approximately +/-4.3% and results for Evangelicals only have a margin of error of approximately +/-4.2%. Margins of error are based on raw, unweighted sample size.
The survey was in the field from 4/4-4/12, 2015. However, there was NO calling on Easter Sunday. Phone calls were made during weekday evenings, all day Saturday, and Sunday afternoon and evening (except Easter Sunday). 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-moms, 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).
survey used (1) Registration Based Sample (RBS) of previous
GOP 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.
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.
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.
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.