Final answer:
The statement 'The results are probably biased' is true due to potential non-response bias, while the other statements regarding stratified sampling, the survey result's lack of bias, and the sample being a volunteer sample are false based on the scenario descriptions.
Step-by-step explanation:
In the scenario described, where a random sample of college students is taken and only 50% return the survey form, several statements are presented and need to be classified as true or false:
-The results are probably biased: This is true. Even though the initial sample was random, the fact that only 50% of those sampled returned the form introduces a potential for bias because the responses may not fully represent the overall student population.
-This is an example of stratified sampling: This is false. The scenario doesn't mention dividing the population into subgroups or strata and then choosing a representative sample from each, which would be characteristic of stratified sampling.
-The results of the survey are unbiased because there was a random sample: This is false. The randomness of the initial sample does not guarantee unbiased results if only a subset of those sampled (such as the 50% who returned the forms) participates in the survey.
-This is a volunteer sample: This is false. A volunteer sample involves participants choosing to be part of the sample on their own initiative, whereas in this case, the students were randomly selected, although subsequently, only some chose to respond.
Overall, while the initial sampling methodology may have been random, the final results can be biased due to the non-response bias introduced by only a subset of the sampled population actually participating in the survey.
The complete question is:
A random sample of the students of a college is carefully constructed, and all of the selected students are sent a survey form. 50% of the students return the form. Identify all of the true statements among the following.
The results are probably biased.
This is an example of stratified sampling.
The results of the survey are unbiased because there was a random sample.
This is a volunteer sample.