September 2015 Winthrop Poll of SC Residents
The September 2015 Winthrop Poll interviewed 963 adults (aged
18 and older) living in South Carolina. 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 GOP and
Leaners only have a margin of error of approximately +/-4.8%. Results for Democrats and Leaners only have a margin of error of approximately +/-5.3%. Results for whites only have a margin of error of approximately +/-3.8%. Results for blacks only have a margin of error of approximately +/-6%. Margins of error are based on weighted
sample size. 48% of the weighted respondents
came from wireless (i.e. cell phone) sample.
The survey was in the field from 9/19-9/27, 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-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
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. Both the RDD sample and the wireless sample were purchased
from Survey Sampling International (SSI). A further explanation of RDD
methodology, with descriptions taken from SSI’s website, may be found below.
Questionnaires were administered in English.
Phone numbers selected for the survey were re-dialed up to five times in an attempt to reach a respondent. Once a household was reached,
we also employed procedures to randomize within households for RDD sample.
1. Weight responses based on sex, age, and race according to
the known population of residents of SC age 18 and older.
2. Randomize within household for respondents reached via
RDD sample. Households are randomly designated for respondent selection based
on the oldest/youngest male/female adult living in the household.
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
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.