# How to find critical value for one-sided and two-sided t test in R?

R ProgrammingServer Side ProgrammingProgramming

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

Live Demo

qt(0.05,30)

## Output

 -1.697261

Right side critical value with sample size 30 and 95% confidence level −

## Example

Live Demo

abs(qt(0.05,30))

## Output

 1.697261


## Example

Live Demo

qt(0.05,50)

## Output

 -1.675905

## Example

Live Demo

abs(qt(0.05,50))

## Output

 1.675905


## Example

Live Demo

qt(0.01,50)

## Output

 -2.403272

## Example

Live Demo

abs(qt(0.01,50))

## Output

 2.403272


## Example

Live Demo

qt(0.01,51)

## Output

 -2.401718

## Example

Live Demo

abs(qt(0.01,51))

## Output

 2.401718


## Example

Live Demo

qt(0.01,100)

## Output

 -2.364217

## Example

Live Demo

abs(qt(0.01,100))

## Output

 2.364217


## Example

Live Demo

qt(0.01,20)

## Output

 -2.527977

## Example

Live Demo

abs(qt(0.01,20))

## Output

 2.527977


## Example

Live Demo

qt(0.10,36)

## Output

 -1.305514

## Example

Live Demo

abs(qt(0.10,36))

## Output

 1.305514


Two-sided critical value for 90% confidence level with sample size of 36 −

## Example

Live Demo

abs(qt(0.10/2,36))

## Output

 1.688298

## Example

Live Demo

abs(qt(0.01/2,101))

## Output

 2.625386


## Example

Live Demo

abs(qt(0.05/2,89))

## Output

 1.986979