[Kon-Peki]

No it is not correct.

"the 90 students who did respond to the questionnaire are representative of the entire population"

How can anyone know this without knowing the size of the freshman class? For that matter, how does anyone know that 120 would have been a good number?

[scottcodie]

The more people you survey, the higher the confidence that the questionnaire is representative of the entire population, or the 'confidence interval'. Since the population was randomly sampled & non-responses don't correlate to the topic questions, you can assume that the 90 students are representative of the entire population with +- some confidence interval.

[Kon-Peki]

Yes, but we know neither the size of the population nor the confidence interval had the full 120 students responded.

Secondly, non-responses may actually correlate to the topic questions! For all anyone knows, students may not respond because

- too busy studying

- too busy partying

- too busy with intramural sports

- too disillusioned, feeling that it will not make a difference.

Etc