This tutorial offers a glimpse into the fundamentals of public opinion polling. Designed for the novice, Polling Fundamentals provides definitions, examples, and explanations that serve as an introduction to the field of public opinion research.
Common sampling processes

Sampling

What is a scientific sample?

A scientific sample is a process in which the respondents are chosen randomly by one of several methods. The key component in the scientific sample is that everyone within the designated group (sample frame) has a chance of being selected.


How are the surveys conducted?

Two of the most common ways that public opinion polls are conducted include: telephone and/or face-to-face interviews. Other methods include mail, on-line and self-administered surveys.


How is the sample selected for a telephone survey?

Typically, survey organizations conducting telephone surveys purchase a Random Digit Dial (RDD) sample of randomly-generated phone numbers from a firm that specializes in designing samples that have been purged to eliminate business numbers, dead lines, etc. Much could be said on this topic, but to keep it simple, a 10-digit phone number in the United States consists of 4 parts.

The Dissection of a Telephone Number

(777)

777

77

77

(Area Code)

Exchange

Block Number

RANDOMLY GENERATED NUMBERS

All 4 components are assigned by the telephone company. The first 3 components are based on location and the final component is randomly generated.

The interviewer will then randomly select a person in the household to be interviewed. One common method is to ask for the adult in the household who had the most recent birthday. This is done because it is an easy way to obtain a random respondent from the household, rather than the first person to answer the phone.
In addition, certain parts of the population, such as young males, are more difficult to get on the phone than others, such as the elderly. Because of this, interviewers often ask to speak with the youngest male in a household first.

Because nearly a quarter of the US population (as of 2014) has a cell phone but no landline telephone, true scientific samples should include a subsample of cell phone users. Cell phone sampling comes with its own unique challenges, such as higher cost and lower response rates. FCC regulations require that cell phone lines be dialed by hand, rather than computer, increasing time and manpower requirements. Geographic information is also different for cell phones, with the area code offering the only geographic information for the cell phone user, and the exchange and block numbers offering information on the service provider.  In addition, the portability of cell phones means that users can keep their numbers if they move. Despite these added complications, however, cell phone sampling methods are similar to those used for landline telephones.


How are face-to-face samples selected?

Face-to-face surveys, also known as ‘in-person’ interviews, are conducted with the interviewer and the interviewee next to each other. The interviewer reads material from the questionnaire and records the responses. At times the interviewer may hand a card to the respondent for him/her to select response(s).

Scientific face-to-face surveys are normally conducted using geographic area probability sampling. Some refer to this as ‘block sampling’. Selecting a sample to represent your targeted population can be tedious work. The method used is referred to as multi-stage sampling. The population frame is first identified by blocks. For instance, you are starting a new business in Cincinnati, and you want to find out how many households have various items. You need to identify the sampling frame. In this case, to make the job cost effective, you divide the city into 1,000 ‘blocks’ based on size so each block has roughly the same number of adults. Within each block there are 250 housing units. In order to get 500 completed interviews, with an estimated 80% completion rate, you first randomly choose 25 blocks, then randomly choose 25 housing units within each block. Once at the housing unit level, the final step is to randomly choose a respondent within the household.


What’s a self-administered survey?

In a self-administered survey, the respondent is directly handed the questionnaire to fill out. Exit polls are examples of self-administered surveys. Voters leaving polling booths are randomly selected to fill out a questionnaire in this type of survey.
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