A special case arises in statistics when the sample size is small, when it can be assumed that the population being investigated is normally distributed, and when the population standard deviation is unknown and must be estimated by the sample standard deviation. Appendix C, Table C.3 shows values taken from the t distribution. Note that only one value need be specified before referring to the table, namely, the degrees of freedom (abbreviated df). Once the degrees of freedom is known, the t values that example