A researcher planning a survey of heads of households in a particular state has census lists for each of the 23 counties in that state. He plans to obtain a random sample from each of the counties rather than grouping all census lists together and obtaining a sample from the entire group. Which of the following statements about the resulting stratified sample are true?

I. It is not a simple random sample.
II. It will help to avoid samples that do not represent the population.
III. It provides comparative information (e. g. mean salary of County X vs County Y) that a simple random sample would not provide.

I only
I and II
I and III
I, II, and III
None of the above

Stu and ambrose are working together on a study of whether diet is related to students' mental health. first, they randomly select 10 students from the student center and 10 students from the office of counseling and psychological services. then, they ask students to rate their diet in terms of healthiness on a scale of 1-100 before completing a 20-item mental health survey. a) name one of the constructs being studied b) how was the construct you named above operationally defined in this experiment? e) was the variable you described above their independent variable, their dependent variable, or a controlled variable? d) what is a confounding variable? what is a potential confound in this study?