- 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**

Which statement(s) regarding the selection of an appropriate sample size is (are) false?

II. If the population is normally distributed and the population variance is unknown, use a z-score irrespective of sample size.

III. If the population is not normally distributed and the population variance is known, use a F-score only if n >= 30; otherwise it cannot be done.

IV. If the population is not normally distributed and the population variance is unknown, use a X

I. If the population is normally distributed and the population variance is known, use a t-score irrespective of sample size.

II. If the population is normally distributed and the population variance is unknown, use a z-score irrespective of sample size.

III. If the population is not normally distributed and the population variance is known, use a F-score only if n >= 30; otherwise it cannot be done.

IV. If the population is not normally distributed and the population variance is unknown, use a X

^{2}-score only if n >= 30; otherwise it cannot be done.A. I and II

B. II, III and IV

C. I, II, III and IV

**Explanation:**All these statements are false. The correct statements would have been:

- If the population is normally distributed and the population variance is known, use a z-score irrespective of sample size.
- If the population is normally distributed and the population variance is unknown, use a t-score irrespective of sample size.
- If the population is not normally distributed and the population variance is known, use a z-score only if n >= 30; otherwise it cannot be done.
- If the population is not normally distributed and the population variance is unknown, use a t-score only if n >= 30; otherwise it cannot be done.

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**User Contributed Comments**
4

User |
Comment |
---|---|

kellyyang |
population variance unknown, using t-score population variance known, using z-score population variance known, if n>30, using z-score population variance unknown, if n<30, using t-score |

kellyyang |
SOrry one i typed wrong. correct is n>30, using t-score for unknown. |

lordcomas |
Memorize these 4 bullet points and you will be safe for answering related questions. |

swkimpo |
For reference, F-score is used to determine whether two variances are the same. A chi-square score is used to test a single variance. |