Methodology

How Does the Gallup World Poll Work?

Measures the Attitudes and Behaviors of the World's Residents

Since creating the World Poll in 2005, Gallup has conducted studies in more than 160 countries that include 99% of the world's adult population.

The Gallup World Poll tracks the most important issues worldwide, such as food access, employment, leadership performance, and well-being. Gallup Senior Scientists advise on the development of a common set of statistics Gallup collects in every country in the world. The World Poll survey includes more than 100 global questions as well as region-specific items. Gallup asks residents from Australia to Pakistan the same questions, every time, in the same way. This makes it possible to trend data from year to year and make direct country comparisons.

How are interviews conducted for the Gallup World Poll?

Gallup uses telephone surveys in countries where telephone coverage represents at least 80% of the population or is the customary survey methodology. In countries where telephone interviewing is employed, Gallup uses a random-digit-dial (RDD) method or a nationally representative list of phone numbers. Telephone methodology is typical in the U.S., Canada, Western Europe, Japan, Australia, etc. Gallup purchases telephone samples from various sample providers located in each region, including Sample Answers and Sample Solutions.

In the developing world, including much of Latin America, the former Soviet Union countries, nearly all of Asia, the Middle East, and Africa, Gallup uses an area frame design for face-to-face interviewing in randomly selected households.

Face-to-face interviews are approximately one hour, while telephone interviews are about 30 minutes.

With some exceptions, all samples are probability based and nationally representative of the resident population aged 15 and older. The coverage area is the entire country including rural areas, and the sampling frame represents the entire civilian, non-institutionalized adult population of the country. Exceptions include areas where the safety of the interviewing staff is threatened and scarcely populated islands in some countries. Sampling procedures include the following stages:

  • STEP 1 -- Selecting Primary Sampling Units (PSUs): In countries where Gallup conducts face-to-face surveys, the first stage of sampling is the identification of PSUs, consisting of clusters of households. PSUs are stratified by population size and/or geography and clustering is achieved through one or more stages of sampling. Where population information is available, sample selection is based on probabilities proportional to population size; otherwise, Gallup uses simple random sampling. In countries where telephone interviewing is employed, Gallup uses a RDD method or a nationally representative list of phone numbers. In select countries where cellphone penetration is high, Gallup uses a dual sampling frame. Gallup makes at least three attempts to reach a person in each household.
  • STEP 2 -- Selecting Households: Gallup uses random-route procedures to select sampled households. Unless an outright refusal occurs, interviewers make up to three attempts to survey the sampled household. To increase the probability of contact and completion, interviewers make attempts at different times of the day, and when possible, on different days. If the interviewer cannot obtain an interview at the initial sampled household, he or she uses a simple substitution method.
  • STEP 3 -- Selecting Respondents: In face-to-face and telephone methodologies, random respondent selection is achieved by using either the latest birthday or Kish grid method. In a few Middle Eastern and Asian countries, gender-matched interviewing is required, and probability sampling with quotas is implemented during the final stage of selection. Gallup implements quality control procedures to validate the selection of correct samples and that the interviewer selects the correct person in each household.

How many people are interviewed in a typical World Poll survey?

The typical survey includes at least 1,000 individuals. In some countries, Gallup collects oversamples in major cities or areas of special interest. Additionally, in some large countries, such as China and Russia, sample sizes of at least 2,000 are collected. Although rare, in some instances, the sample size is between 500 and 1,000.

How often is the Gallup World Poll conducted?

Gallup conducts World Poll surveys on a semiannual, annual, and biennial frequency that is determined on a country-by-country basis.

Are Gallup World Poll samples weighted?

Yes, Gallup weights World Poll samples to correct for unequal selection probability, nonresponse, and double coverage of landline and cellphone users when using both cellphone and landline frames. Gallup also weights its final samples to match the national demographics of each selected country. The margin of error for each sample reflects the influence of data weighting. In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.

Where can I find results from the Gallup World Poll and learn more about the survey?

Gallup regularly publishes newsworthy World Poll findings on Gallup.com. Sign up for Gallup News alerts to get these articles as soon as they are published.

For more detailed information about each country included in the Gallup World Poll and the most recent data collection activities in each country, read the Country Data Set Details. For questions about how these surveys are conducted, please contact galluphelp@gallup.com.

To access World Poll data to compare residents' responses to questions on topics such as economic conditions, government and business, health and well-being, infrastructure, and education, subscribe to Gallup Analytics.

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