How Do I Determine T Critical Value?

A T-critical value is used in statistics to construct a confidence interval, a range of values that is likely to include a parameter being studied. To find a critical value, you need to know the alpha value and degrees of freedom.

Alpha Values

An alpha value is an indication of whether an event may have occurred by chance. An alpha value is found by subtracting the confidence level from 1, then dividing by 2. For example, if you wanted your confidence level to be 98 percent, then (1 - 0.98) / 2 = .001.

Degrees of Freedom

Degrees of freedom is the number of values in your statistical calculation that can vary. Degrees of freedom can be found by subtracting 1 from your sample size. For example, if there are nine items in your sample, then 9-1=8.

T-Table

Determine the T-critical value by looking up the the degrees of freedom (df) and alpha level (α) in a T-table. The T-critical value is the intersection of the df row and the α column.

References

• How to Find a Confidence Interval for a Sample

Resources

• T-Distribution Table