Question

a researcher is interested in studying the possible relationship between a person’s yearly income and whether or not they need to wear corrective lenses. to investigate, the researcher conducts an observational study by surveying a sample of 500 adults who are currently employed full - time and records whether or not the participant needs to wear corrective lenses, age, and the participant’s yearly income. then he compares the average yearly income between the two groups.
(a) why might the researcher have chosen to perform an observational study (by conducting a survey) and not a randomized experiment (by assigning participants to either the corrective lenses group or no corrective lenses group at random)? choose the best answer from the choices below.
○ for a randomized experiment to be performed, the researcher would have to randomly assign participants to either the corrective lenses group or the no corrective lenses group. but whether or not a person needs to wear corrective lenses is out of the researcher’s control.
○ a randomized experiment should never be performed when it is possible to perform an observational study. when groups are randomly assigned, the researcher cannot control the types of participants in each group, making the results of a randomized experiment unreliable.
○ for a randomized experiment to be performed, the researcher must ask people in the population to volunteer to take part. this would mean that there would not be any chance to include people who wear corrective lenses in the sample.

Explanation:

A randomized experiment would require assigning participants to wear or not wear corrective lenses, but this factor (needing corrective lenses) is outside the researcher's control; participants have a pre-existing need or not, so random assignment to these groups is not feasible or ethical. The other options are incorrect: observational studies can be done alongside randomized experiments when appropriate, random assignment does not make results unreliable, and volunteer bias is not the core reason here.

Answer:

For a randomized experiment to be performed, the researcher would have to randomly assign participants to either the corrective lenses group or the no corrective lenses group. But whether or not a person needs to wear corrective lenses is out of the researcher's control.