- CFA Exams
- CFA Level I Exam
- Study Session 3. Quantitative Methods (2)
- Reading 10. Sampling and Estimation
- Subject 6. Confidence Intervals for the Population Mean

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**CFA Practice Question**

Consider the following statements relating to sample size and confidence intervals:

II. When the width of a confidence interval decreases, this is due to standard error becoming smaller.

III. More precise results are obtained when the sample size is increased.

I. The width of a confidence interval decreases as the sample size increases.

II. When the width of a confidence interval decreases, this is due to standard error becoming smaller.

III. More precise results are obtained when the sample size is increased.

Which is true?

A. II and III

B. I and III

C. I, II and III

**Explanation:**The following statements relate to sample size and confidence intervals:

- The width of a confidence interval decreases as the sample size increases.
- When width of a confidence interval decreases, this is due to standard error becoming smaller.
- More precise results are obtained when the sample size is increased.

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