CONFIDENCE_T
Updated: 31 July 2015
Use CONFIDENCE_T to calculate a confidence interval when you don't know the population standard deviation and are using the sample standard deviation instead.
Syntax
SELECT [wct].[CONFIDENCE_T](
<@Alpha, float,>
,<@Standard_dev, float,>
,<@Size, float,>)
Arguments
@Alpha
The significance level used to calculate the confidence interval. @Alpha must be of a type float or of type that intrinsically converts to float.
@Standard_dev
The sample standard deviation. @Standard_dev must be of a type float or of a type that intrinsically converts to float.
@Size
The sample size. @Size must be of a type float or of a type the intrinsically converts to float.
Return Type
float
Remarks
· 0 < @Alpha < 1
· 0 < Standard_dev
· 0 < @Size
Examples
Given a sample standard deviation of 14.67, calculate the 95% confidence interval for a sample size of 50.
SELECT
wct.CONFIDENCE_T(
.05 --@Alpha
,14.67 --@Standard_dev
,50 --@Size
) as CI
This produces the following result
The CONFIDENCE_T function is closely related to the T_INV function.
SELECT
wct.CONFIDENCE_T(alpha,mu,sigma) as CI
,wct.T_INV(1-alpha*0.5,sigma-1)*mu/SQRT(sigma) as CI
FROM (VALUES(0.05,14.67,50))n(alpha,mu,sigma)
This produces the following result.
See Also