SOLUTION: In a study using 13 samples, and in which the population variance is unknown, the distribution that should be used to calculate confidence intervals is A) a standard normal distri

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Question 727231: In a study using 13 samples, and in which the population variance is unknown, the distribution that should be used to calculate confidence intervals is
A) a standard normal distribution.
B) a t distribution with 12 degrees of freedom.
C) a t distribution with 13 degrees of freedom.
D) a t distribution with 14 degrees of freedom.

Answer by jim_thompson5910(35256) (Show Source):
You can put this solution on YOUR website!
The population variance is unknown. So the population standard deviation is also unknown (since variance = (standard deviation)^2)

So because the the population standard deviation is unknown AND the sample size n is less than 30, this means that you must use the T distribution.

In this case, you would use a T distribution with degrees of freedom (df) of...

df = n-1

df = 13-1

df = 12

So the answer is B) a t distribution with 12 degrees of freedom