The formulae for the critical values involve the quantile function Q which is the inverse of the cumulative distribution function cdf for the test statistic. Subtract the confident interval from 100 and convert the resultant into a decimal value to get the alpha. How To Read Values On A Chi Square Critical Value Table Chi Square Square Reading The following steps will guide on how to calculate the critical value of Z. . Degree of freedom 30. Significance level 5 5100 005. The steps to find the critical value using a confidence interval are as follows. Using the alpha value from the first formula calculate the critical probability. If you are constructing a 95 confidence. It describes how far from the mean of the distribution you have to go to cover a certain amount of the total variation in the data ie. To find the critical t value one needs to compute the inverse cumulative PDF of the T distribution. The ...