### CFA Practice Question

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### CFA Practice Question

You are thinking of using a t procedure to construct a 95% confidence interval for the mean of a population. You suspect that the distribution of the population is not normal and may be skewed. Which of the following statements is correct?

A. You should not use the t procedure because the population does not have a normal distribution.
B. You may use the t procedure, provided your sample size is large, say, at least 30.
C. You may use the t- procedure because it is robust to non-normality.

t procedures are robust against non-normality of the population except in the case of outliers or strong skewness. Guidelines are:
• sample size less than 15: use a t procedure if the data are close to normal. If the data are clearly not normal or if outliers are present, do not use a t procedure.
• sample size at least 15: a t procedure can be used except in the presence of outliers or strong skewness.
• large samples: t procedures can be used even for clearly skewed distributions when the sample is large, roughly n >= 30.