When is a survey representative? Each survey is a representative survey. The real question is: Representative of what?
Many erroneously believe large samples make surveys representative, but it is not true. Large samples reduce the error level associated with the answers. In fact, at the 95% confidence interval both samples of 96 and 9’512 interviews may be representative of the population they are drawn from. The difference lies in the error level, 10% for the former sample and 1% for the other.
What ultimately makes a survey representative is its ability to reproduce the characteristics of the population it comes from.
This means the way interviewees are selected is what really impacts the ability of a survey to represent the population it refers to.
If our survey is supposed to estimate the median height of Californian women and we measure 9’512 women living in Los Angeles, no matter how large the sample, the survey will not be representative of the Californian women.
The cross-tables of the fix data is usually a good place to start looking for evidence concerning the representativeness of a survey.