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Which situation is an example of an observational study?

If answer is correct I will mark as brainliest

A. Having customers fill out a questionnaire about their favorite brand of toothpaste

B. Collecting the blood pressure readings of a group of elderly individuals in a small town

C. Dividing a class into thirds, giving each third a different amount of time to read, and then testing comprehension

D. Testing the effectiveness of a mouthwash by allowing one group to use it and comparing the results with those of a group that doesn't use it

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Respuesta :

Answer:

D

Step-by-step explanation:

An observational study is conducted by drawing inferences from a sample to a population where the independent variable is not under the control of the researcher.

One common observational study is about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator.

The best option which fits the description :

Testing the effectiveness of a mouthwash by allowing one group to use it and comparing the results with those of a group that doesn't use it.

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