Well typically a researcher will want to ensure those that completed the survey are comparable to the population, in order to potentially generalize. You would then select variables of interest that may affect survey results and display that both groups are the same, in order to rule out dissimilarities. Perhaps demographics fit this need. So you compare the ages, race, grades, etc. between the sample and the population to show there are no differences. So for comparing ages (continous variable) you may use ttests or Wilcoxon rank sums and for race (categorical) you may use chi-square or Fisher's exact test. So how the data are formatted dictates the tests you may use to compare the sample to the population.

Lastly you may also need to run some power or sample size calculations to ensure that you have a large enough sample to ensure that if there was a difference, that your statistical test would be powered sufficiently to discern this.