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# How to Find t Critical Values in R

Whenever you conduct a t-test, you will get a test statistic as a result. To determine if the results of the t-test are statistically significant, you can compare the test statistic to aÂ tÂ critical value. If the absolute value of the test statistic is greater than the t critical value, then the results of the test are statistically significant.

The t critical value can be found by using aÂ t distribution tableÂ or by using statistical software.

To find the t critical value, you need to specify:

• A significance level (common choices are 0.01, 0.05, and 0.10)
• The degrees of freedom

Using these two values, you can determine the t critical value to be compared with the test statistic.

### How to Find the T Critical Value in R

To find the T critical value in R, you can use the qt()Â function, which uses the following syntax:

qt(p, df, lower.tail=TRUE)

where:

• p:Â The significance level to use
• df: The degrees of freedom
• lower.tail:Â IfÂ TRUE, the probability to the left ofÂ pÂ in the t distribution is returned. If FALSE, the probability to the right isÂ returned. Default is TRUE.

The following examples illustrate how to find the t critical value for a left-tailed test, right-tailed test, and a two-tailed test.

### Left-tailed testÂ

Suppose we want to find the t critical value for a left-tailed test with a significance level of .05 and degrees of freedom = 22:

```#find t critical value
qt(p=.05, df=22, lower.tail=TRUE)

[1] -1.717144
```

The t critical value isÂ -1.7171. Thus, if the test statistic is less than this value, the results of the test are statistically significant.

### Right-tailed testÂ

Suppose we want to find the t critical value for a right-tailed test with a significance level of .05 and degrees of freedom = 22:

```#find t critical value
qt(p=.05, df=22, lower.tail=FALSE)

[1] 1.717144
```

The t critical value isÂ 1.7171. Thus, if the test statistic is greater than this value, the results of the test are statistically significant.

### Two-tailed testÂ

Suppose we want to find the t critical values for a two-tailed test with a significance level of .05 and degrees of freedom = 22:

```#find two-tailed t critical values
qt(p=.05/2, df=22, lower.tail=FALSE)

[1] 2.073873
```

Whenever you perform a two-tailed test, there will be two critical values. In this case, the T critical values areÂ 2.0739Â andÂ -2.0739. Thus, if the test statistic is less than -2.0739 or greater than 2.0739, the results of the test are statistically significant.

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