Global Findex Database Survey Methodology
The indicators in the Global Financial Inclusion (Global Findex) Database are drawn from survey data covering more than 150,000 people in 148 economies—representing more than 97 percent of the world’s population (a list of economies included is available here). The survey was carried out over the 2011 calendar year by Gallup, Inc. as part of its Gallup World Poll, which since 2005 has surveyed approximately 1,000 people annually in up to 157 economies, using randomly selected, nationally representative samples. The target population is the entire civilian, noninstitutionalized population age 15 and older. Surveys are conducted in the major languages of each economy.
Surveying is conducted face-to-face in economies where telephone coverage represents less than 80 percent of the population or is the customary methodology. In most economies the fieldwork is completed in two to four weeks. In economies where face-to-face surveys are conducted, the first stage of sampling is the identification of primary sampling units. These units are stratified by population size, geography, or both, 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, simple random sampling is used. Random route procedures are used to select sampled households. Unless an outright refusal occurs, interviewers make up to three attempts to survey the sampled household. If an interview cannot be obtained at the initial sampled household, a simple substitution method is used. Respondents are randomly selected within the selected households by means of the Kish grid or latest birthday method. In economies where cultural restrictions dictate gender matching, respondents are randomly selected using the Kish grid from among all eligible adults of the interviewer’s gender.
In economies where telephone interviewing is employed, random digit dialing (RDD) or a nationally representative list of phone numbers is used. In selected economies where cell phone penetration is high, a dual sampling frame is used. Random respondent selection is achieved by using either the latest birthday or Kish grid method. At least three attempts are made to reach a person in each household, spread over different days and times of day.
Data weighting is used to ensure a nationally representative sample for each economy. Final weights consist of the base sampling weight, which corrects for unequal probability of selection based on household size, and the poststratification weight, which corrects for sampling and nonresponse error. Poststratification weights use country-level population statistics on gender and age and, where reliable data are available, education or socioeconomic status.
The margin of error is calculated around a proportion at the 95 percent confidence level. The maximum margin of error was calculated assuming a reported percentage of 50 percent and takes into account the design effect. Margin of error calculation: √(0.25/N)*1.96*√(DE). In economies where gender-matched interviewing was implemented, the margin of error should be inflated to approximate the effect of nonrandom procedures during the final stage of sampling. Margins of error that take into account the design effect and intraclass correlation for individual statistics, by economy, can be found in Demirguc-Kunt and Klapper (2012).Other errors that can affect survey validity include measurement error associated with the questionnaire, such as translation issues, and coverage error, where a part of the target population has a zero probability of being selected for the survey.
The data collection period, number of interviews, approximate design effect, and margin of error, as well as sampling details for each economy, is available here.
Additional information about the methodology used in the Gallup World Poll can be found at https://worldview.gallup.com/content/methodology.aspx.
The reference citation for the Global Findex data is Asli Demirguc-Kunt and Leora Klapper, 2012. “Measuring Financial Inclusion: The Global Findex Database.” World Bank Policy Research Working Paper 6025.