as the standard normal distribution, but it reflects the greater variability that is expected with small samples. 4. t distributions are used with small samples or when is not known. Example of degrees of freedom: If 10 test scores have the restriction that their mean is 80, then their sum must be 800, and we can freely assign values to the first 9 scores, but the 10th score would then be determined, so in this case there are 9 degrees of freedom How many degrees of freedom are there for a sample size of 34? Use the critical values of t-table to find the critical value of t for a sample size of 34 when building a 90% confidence interval. To find critical values of t on Excel use the following function. =T.INV(probability to left of critical value, degrees of freedom)