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How to find critical value for one-sided and two-sided t test in R?
To find the critical value for t test in R, we need to use qt function. This function requires level of significance and the sample size and returns the tabulated or critical value of t distribution. Below examples shows the calculation of critical value for different situations such as left-side test, right-side test or two-sided test.
Left side critical value with sample size 30 and 95% confidence level −
Example
qt(0.05,30)
Output
[1] -1.697261
Right side critical value with sample size 30 and 95% confidence level −
Example
abs(qt(0.05,30))
Output
[1] 1.697261
Example
qt(0.05,50)
Output
[1] -1.675905
Example
abs(qt(0.05,50))
Output
[1] 1.675905
Example
qt(0.01,50)
Output
[1] -2.403272
Example
abs(qt(0.01,50))
Output
[1] 2.403272
Example
qt(0.01,51)
Output
[1] -2.401718
Example
abs(qt(0.01,51))
Output
[1] 2.401718
Example
qt(0.01,100)
Output
[1] -2.364217
Example
abs(qt(0.01,100))
Output
[1] 2.364217
Example
qt(0.01,20)
Output
[1] -2.527977
Example
abs(qt(0.01,20))
Output
[1] 2.527977
Example
qt(0.10,36)
Output
[1] -1.305514
Example
abs(qt(0.10,36))
Output
[1] 1.305514
Two-sided critical value for 90% confidence level with sample size of 36 −
Example
abs(qt(0.10/2,36))
Output
[1] 1.688298
Example
abs(qt(0.01/2,101))
Output
[1] 2.625386
Example
abs(qt(0.05/2,89))
Output
[1] 1.986979
Updated on: 10-Oct-2020
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