The T table shows values of critical T values that correspond to Degree of Freedom and Level of significance of the test.
Degree of Freedom
The Degree of freedom or DF is calculated with the simple formula:
DF = n – 1
where n = sample size
Level of Significance
The level of significance is most commonly known as ALPHA value of the statistical study. The alpha level is decided by the statistician in charge of the study or experiment taking place. The most common values of Alpha are 0.1, 0.05, 0.025, and 0.01
The table given below goes to a higher degree of accuracy with the smallest alpha value of 0.0005
What are Tails?
T tests are of two types. One tailed T test and and Two Tailed T test. The tail defines the location of the rejection region of the statistical test. A one tailed test may has only one rejection region on either the left or right side of the distribution curve. The figures Below show the distinction between a single tailed test and a two tails test.
Understanding the Table
The top Rows of the T table give us the alpha values of the T test. Select the appropriate alpha value and look down that column.
The Left column show the degree of freedom for the sample in the study. Match the value of alpha and Degree of Freedom to get the correct Critical T value for the T test.
The Bottom row shows confidence interval in percentage values. Use the Bottom row and Degree of Freedom values to get the correct Critical T value for Confidence interval studies.
I got the Critical T value, Now What?
The critical T value must be compared with the value of the T score
Click here to see the formula for T score calculation.
If Critical T value > T score, Then reject null hypothesis of the T test
If Critical T value < T score, then Fail To Reject null hypothesis of T test.
Click here for more information on T table and how to use it.