A school wants to determine if students think that prom tickets are too expensive. Because only juniors and seniors can attend prom, the school pulls a simple random sample of the juniors and seniors of the school to participate in the study.



This method of sampling is likely to be:


Biased, because systematic sampling should have been used to contact employees.


Biased, because the two groups are different in character.


Unbiased, because the population has been stratified by telephone number.

Saved
Unbiased, because it is an example of stratified random sampling.