Sample composition

Few people know, but the composition of a statistic sample is what differentiates a research from a survey. While the survey listens to people who are self-selected, arbitrarily, researches are done with a statistic representing sample.

The construction of the sample starts with the analysis of the secondary data, that detail the social economic profile of the population. These are large collection of data from the Brazilian Institute of Geography and Statistics (IBGE): the Census and the National Survey by Household Samples (Pnad). With this information, IBOPE knows where to find the people that should be part of a sample representing ta universe.

However, more updated official data do not yet meet IBOPE needs. To complement this material, the company carries out the Social Economic Study (LSE), with more than 10 thousand interviews a year, in an effort to have more precise samples.

Normally, the process to build a sample involves several steps. In a national research, for instance, almost all capitals of the country are selected. Then, there are drawings to select municipalities to represent the countryside of the states. After that, new drawings are prepared to define census sectors of each municipality.

Then on, researches start to look for a number of people that may represent proportionally the population, based on criteria including field of activity, education level, age group, and gender. Then, we find a sample considered to be a picture of the universe it represents.

For safety purposes, IBOPE field team also checks in census sectors, prior to running the interviews, to check if buildings and houses are according to or outdated compared to secondary data.

 
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