which situation is an example of an observati...
which situation is an example of an observational study?\na. having customers fill out a questionnaire about their favorite brand of toothpaste\nb. testing the effectiveness of a mouthwash by allowing one group to use it and comparing the results with those of a group that doesnt use it\nc. dividing a class into thirds, giving each third a different amount of time to read, and then testing comprehension\nd. collecting the blood pressure readings of a group of elderly individuals in a small town
Answer
# Answer:
D. Collecting the blood pressure readings of a group of elderly individuals in a small town
# Brief Explanations:
An observational study just observes and records data without interfering or manipulating variables. In A, it's a survey. In B and C, there are interventions (using mouth - wash, different reading times). In D, only blood - pressure readings are collected without any manipulation.