Question

1. a medical researcher reports that the average recovery time from a treatment is 14 days ± 2 days at a 95% confidence level. which statement is correct? a. the margin of error is unrelated to the confidence level. b. increasing the confidence level will reduce the margin of error. c. repeating the study with the same sample size will reduce the margin of error. d. decreasing the confidence level will reduce the margin of error. 8. a farmer applies different amounts of water to three groups of crops and compares how much they grow. this is an example of: a. an experiment b. a sample survey c. a random phenomenon d. an observational study 9. a teacher surveys 200 students about their sleep habits by asking them to complete an online questionnaire. she records how many hours of sleep they report each night. which two can be concluded? a. the study used random assignment of students. b. the study was based on self - reporting. c. the study has an observational design. d. the study used an experimental design. e. the study collected objective measurements.

Explanation:

• For question 7: The margin of error is directly related to the confidence level. Higher confidence levels require a larger margin of error. Decreasing the confidence level will reduce the margin of error.
• For question 8: The farmer is manipulating the independent variable (amount of water) and observing the dependent variable (crop growth), which is characteristic of an experiment.
• For question 9: The teacher is asking students to report their sleep - habits via a questionnaire, which is self - reporting. There is no random assignment or experimental manipulation, so it's an observational study based on self - reported data.

Answer:

1. D. Decreasing the confidence level will reduce the margin of error.
2. A. an experiment
3. B. The study was based on self - reporting., C. The study has an observational design.