If the population distribution is unknown, in most cases the sampling distribution of the mean can be approximated by the normal distribution if the sample size is at least 15 observations.

判断题When analyzing categorical data, stem and leaf display is an appropriate plot.

单项选择题X is a discrete random variable that can have values from 0 to infinity, and occurrences of the events X counts are independent. The standard deviation of X is equal to the square root of the mean. The probability distribution of X is a(n) （）distribution.

A.binomial
B.uniform
C.normal
D.Possion

单项选择题The empirical rule tells us that approximately of the values cluster within a distance of 1 standard deviation from the mean for a bell-shaped distribution（）

A.68%
B.95%
C.99.7%
D.none of the above

单项选择题The reason that we prefer the sample standard deviation as our measure of typical variation instead of the sample variance is that（）

A.the variance is not as accurate a measurement as the standard deviation
B.the standard deviation has been corrected for bias while the variance has not
C.the standard deviation is in the same units as the data values.
D.the variance is in the same units as the data values.

单项选择题The sum of the deviations may be 0.00.To get around this problem，we use the（）of the deviations

A.square
B.absolute value
C.minimum
D.maximum