For a two-sided test, find the column corresponding to 1-α/2 and reject the null hypothesis if Critical values of Student's t distribution with ν degrees of freedom . When the sample size is small (less than 30) and/or the population standard deviation is unknown, you use the t-distribution to find critical values. (At roughly A T critical value is a “cut off point” on the t distribution. It's almost identical to the Z critical value (which cuts off an area on the normal.
While the z-score can also be used to calculate probability for unknown standard deviations and small samples, many statisticians prefer to use the t distribution. The right function is TINV(), but the problem is that TINV() assumes that you're inputting the two-tailed probability, not the one-tailed probability. Determine the critical value by finding the value of the known distribution of the The value -t(α/2, n - 1) is the t-value such that the probability to the left of it is.
The mean of a sample is , SEM , sample size What is the 99% confidence interval of the mean? Degrees of freedom (DF) is n−1 = 31, t-value in .