One of the most common questions GeoPoll gets is around how we conduct research through the mobile phone that is nationally representative, meaning results have a high level of accuracy for the population of the country being studied. While GeoPoll uses multiple methods to achieve these goals, including advising on which mobile survey mode to use, one of the most important aspects of our process is the way in which our platform targets respondents based on their demographics. Below we outline what nationally representative samples are, along with some of the steps we take to achieve nationally representative samples in emerging markets throughout Africa, Asia, and Latin America.
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What is a Nationally Representative Sample
A nationally representative sample is one that has a strong enough similarity to the population of the country being studied that results will be valid. This means ensuring that the sample represents the country’s population in key demographic characteristics.
Being that each country has different population compositions, a sample in a survey will vary depending on the country being studied. For example, in Nigeria, the population skews much younger than in the United States, with estimates that half of the Nigerian population are aged 30 or younger. Given this, a study conducted in Nigeria with a sample size of 500 would include 250 respondents who are 30 or younger, whereas the same study conducted in the U.S. or Europe would have a smaller number of respondents from that age bracket, in line with the aging populations in those regions.
How to Build a Nationally Representative Sample
The first step to building nationally representative samples is to determine the most important demographic variables to consider given the project goals and local context. Age, gender, location, and a measure of socioeconomic class are all commonly used variables in building a nationally representative sample. In many countries, race and religion are also important to include to ensure the sample is as similar to the country’s population as possible.
Population data is typically taken from national censuses, but in emerging markets, where census data is often unreliable, determining the makeup of a nationally representative sample can be challenging. To mitigate this, research agencies such as GeoPoll use the most recent widely accepted estimates for population demographics. In countries where national census bureau data is not available, we often use population estimates from the U.S. Census Bureau’s International Data Base, which compiles multiple data sources to create population and demographic projections.
Sample size is also a consideration when thinking about building a nationally representative sample, as larger sample sizes will have higher confidence intervals and lower margins of error. A sample size of around 400 will provide a margin of error of 5% at the 95% confidence level for population sizes above 10,000, and the larger the sample the lower the margin of error becomes.
Once the appropriate sample size and the variables being used to build the sample have been determined, the requirements can be broken down into actual numbers of respondents needed.
In Ghana, a sample size of 400 sample size, nationally representative by age, gender, and location, would look like the below:
- 197 male respondents and 203 female respondents
- 121 aged 16-25, 97 age 26-35, 72 age 36-45, 110 age 46+
- 78 respondents from Ashanti region
- 37 respondents from Brong-Ahafo region
- 36 respondents from Central region
- 43 respondents from Eastern region
- 65 respondents from Greater Accra region
- 40 respondents from Northern region
- 17 respondents from Upper East region
- 34 respondents from Volta region
- 39 respondents from Western region
This sampling technique is also known as quota sampling, and below we explain further how GeoPoll targets specific demographics in our database of respondents to reach the quotas we set for a nationally representative study.
Using Quotas for Nationally Representative Studies in Africa, Asia, and Latin America
Quota sampling can become quite complex depending on the number of variables included, and if they are independent or interlocking, meaning two or more variables are grouped. While GeoPoll’s sampling technique depends on the project specifications, in general, our platform sets limits for each demographic group, which enables us to meet the quotas needed for national representation.
In the example above, to achieve a nationally representative sample of 400, GeoPoll would first send an initial opt-in message to a large group of database members. Depending on the requirements, this initial group may be randomly selected, or we may use demographic information that has been collected from previous GeoPoll surveys users have opted-in to to create a stratified random sample. Once survey responses begin coming in, GeoPoll monitors which quotas are being filled, and closes quotas as the desired sample size per group is achieved. If respondents whose demographics match a quota that has already been filled opt-in to the survey, they are told they are no longer eligible in order to prevent over-representation of that group.
GeoPoll collects, regularly verifies, and securely stores the demographic profiles of our respondents, so that if we have not reached a target for one subgroup, we can recruit more respondents in the necessary subgroup until the targets are met. In cases where budgetary constraints or other factors make reaching the required quotas difficult, GeoPoll can also use weighting to bring the achieved sample more in line with population estimates.
Due to our wide reach in emerging markets, GeoPoll is able to achieve the required demographic quotas needed for nationally representative studies, including reaching respondents in many regions, and of multiple age groups, races, and religions. By using multiple survey modes, including voice calls to access illiterate populations, and in-person enumerators in areas that have little to no mobile connectivity, GeoPoll further ensures that all segments of a population are represented.
To get more detailed information on GeoPoll’s sampling process and learn how we reach nationally representative populations in countries throughout Africa, Asia, or Latin America, please contact us today.