Critical Values of the t Distribution

Critical Values of the t Distribution

graph of t-distribution The probability density function of the t-distribution
The t-distribution is a symmetric distribution and its shape depends on the degrees of freedom (df). The t-distribution has thicker tails than the normal distribution but, as the df increases, the t-distribution approximates the normal distribution. The area under the pdf to the right of t is equal to alpha/2.

d.f.   alpha = .10   alpha = .05
1 6.314 12.706
2 2.920 4.303
3 2.353 3.182
4 2.132 2.776
5 2.015 2.571
6 1.943 2.447
7 1.895 2.365
8 1.860 2.306
9 1.833 2.262
10 1.812 2.228
11 1.796 2.201
12 1.782 2.179
13 1.771 2.160
14 1.761 2.145
15 1.753 2.131
16 1.746 2.120
17 1.740 2.110
18 1.734 2.101
19 1.729 2.093
20 1.725 2.086
21 1.721 2.080
22 1.717 2.074
23 1.714 2.069
24 1.711 2.064
25 1.708 2.060
26 1.706 2.056
27 1.703 2.052
28 1.701 2.048
29 1.699 2.045
30 1.697 2.042
35 1.690 2.030
40 1.684 2.021
45 1.680 2.014
50 1.676 2.009
60 1.671 2.000
70 1.667 1.994
80 1.664 1.990
90 1.662 1.987
100 1.660 1.984
120 1.658 1.980
inf 1.645 1.960

Note: When the df exceeds 30 critical values are not tabulated for every case. For degrees of freedom that are not tabulated, the SHAZAM CONFID command rounds up. For example, with 31 degrees of freedom the critical value for 35 df is used.

Some releases of SHAZAM use critical values that are less accurate for df > 30.


Home [SHAZAM Guide home]