- 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**

A statistician is calculating a confidence interval but the standard deviation of the sampled population is unknown. It is acceptable to use the sample standard deviation in place of the population standard deviation when ______

II. the sample size is greater than 30.

III. the sample distribution behaves according to the central limit theorem.

I. the sample distribution is normally distributed.

II. the sample size is greater than 30.

III. the sample distribution behaves according to the central limit theorem.

A. I and II

B. I and III

C. I, II and III

**Explanation:**

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**User Contributed Comments**
2

User |
Comment |
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CFAToad |
The sample size always behaves according to the central limit theorem, even when N is below 30. |

Steff |
Don't agree with III without the knowledge either that the sample size is >= 30 or the distribution is normal distributed. Every distribution behaves according to the central limit theorem but with a sample size < 30 it is not approximately normal distributed. Other opinions? |