Above all, you need to know who you are trying to represent.

A result is representative when the group of respondents have the same features than another larger group of people.

In order to understand if your results are representative, you need to define what your sample should be representative of : the population of a country, a subset of a population, target consumers of a product, etc.

A Brand lift measure is not representative of the population of a country. It measures the difference in response between two groups : people who have seen your ad, and people who have not seen your ad.

This is why, using the quota method, we are going to look for unexposed respondents who are the same in socio-demographic terms as the exposed respondents. So the only thing that differentiates them is their advertising recall. This is how we can measure the effectiveness of an advertising campaign.