Appendix A. The T-Distribution Table
The t-distribution is a probability distribution with a
symmetrical, bell-shaped curve (similar to the standard normal
curve), the shape of which is affected by a parameter known as the
"degrees of freedom." We used
t-distributions in Chapter 8 of this book to
compute confidence intervals. In that usage, the degrees of freedom
controlled how far out you had to go (in terms of standard
deviations) on the t-distribution curve from the mean to encompass a
given percentage of values. The higher the degrees of freedom, the
larger the interval on the curve.
Table A-1 gives t-distribution values for various
probabilities, with each row representing 1 additional degree of
freedom. Those values in the column for 0.05 (95%) were used in Chapter 8.
Table A-1. The t-distribution table referenced in Chapter 8
| |
0.2
|
0.1
|
0.05
|
0.02
|
0.01
|
0.002
|
0.001
|
|
1
|
3.078
|
6.314
|
12.706
|
31.82
|
63.66
|
318.3
|
637
|
|
2
|
1.886
|
2.92
|
4.303
|
6.965
|
9.925
|
22.33
|
31.6
|
|
3
|
1.638
|
2.353
|
3.182
|
4.541
|
5.841
|
10.21
|
12.92
|
|
4
|
1.533
|
2.132
|
2.776
|
3.747
|
4.604
|
7.173
|
8.61
|
|
5
|
1.476
|
2.015
|
2.571
|
3.365
|
4.032
|
5.893
|
6.869
|
|
6
|
1.44
|
1.943
|
2.447
|
3.143
|
3.707
|
5.208
|
5.959
|
|
7
|
1.415
|
1.895
|
2.365
|
2.998
|
3.499
|
4.785
|
5.408
|
|
8
|
1.397
|
1.86
|
2.306
|
2.896
|
3.355
|
4.501
|
5.041
|
|
9
|
1.383
|
1.833
|
2.262
|
2.821
|
3.25
|
4.297
|
4.781
|
|
10
|
1.372
|
1.812
|
2.228
|
2.764
|
3.169
|
4.144
|
4.587
|
|
11
|
1.363
|
1.796
|
2.201
|
2.718
|
3.106
|
4.025
|
4.437
|
|
12
|
1.356
|
1.782
|
2.179
|
2.681
|
3.055
|
3.93
|
4.318
|
|
13
|
1.35
|
1.771
|
2.16
|
2.65
|
3.012
|
3.852
|
4.221
|
|
14
|
1.345
|
1.761
|
2.145
|
2.624
|
2.977
|
3.787
|
4.14
|
|
15
|
1.341
|
1.753
|
2.131
|
2.602
|
2.947
|
3.733
|
4.073
|
|
16
|
1.337
|
1.746
|
2.12
|
2.583
|
2.921
|
3.686
|
4.015
|
|
17
|
1.333
|
1.74
|
2.11
|
2.567
|
2.898
|
3.646
|
3.965
|
|
18
|
1.33
|
1.734
|
2.101
|
2.552
|
2.878
|
3.61
|
3.922
|
|
19
|
1.328
|
1.729
|
2.093
|
2.539
|
2.861
|
3.579
|
3.883
|
|
20
|
1.325
|
1.725
|
2.086
|
2.528
|
2.845
|
3.552
|
3.85
|
|
21
|
1.323
|
1.721
|
2.08
|
2.518
|
2.831
|
3.527
|
3.819
|
|
22
|
1.321
|
1.717
|
2.074
|
2.508
|
2.819
|
3.505
|
3.792
|
|
23
|
1.319
|
1.714
|
2.069
|
2.5
|
2.807
|
3.485
|
3.768
|
|
24
|
1.318
|
1.711
|
2.064
|
2.492
|
2.797
|
3.467
|
3.745
|
|
25
|
1.316
|
1.708
|
2.06
|
2.485
|
2.787
|
3.45
|
3.725
|
|
26
|
1.315
|
1.706
|
2.056
|
2.479
|
2.779
|
3.435
|
3.707
|
|
27
|
1.314
|
1.703
|
2.052
|
2.473
|
2.771
|
3.421
|
3.69
|
|
28
|
1.313
|
1.701
|
2.048
|
2.467
|
2.763
|
3.408
|
3.674
|
|
29
|
1.311
|
1.699
|
2.045
|
2.462
|
2.756
|
3.396
|
3.659
|
|
30
|
1.31
|
1.697
|
2.042
|
2.457
|
2.75
|
3.385
|
3.646
|
|
32
|
1.309
|
1.694
|
2.037
|
2.449
|
2.738
|
3.365
|
3.622
|
|
34
|
1.307
|
1.691
|
2.032
|
2.441
|
2.728
|
3.348
|
3.601
|
|
36
|
1.306
|
1.688
|
2.028
|
2.434
|
2.719
|
3.333
|
3.582
|
|
38
|
1.304
|
1.686
|
2.024
|
2.429
|
2.712
|
3.319
|
3.566
|
|
40
|
1.303
|
1.684
|
2.021
|
2.423
|
2.704
|
3.307
|
3.551
|
|
42
|
1.302
|
1.682
|
2.018
|
2.418
|
2.698
|
3.296
|
3.538
|
|
44
|
1.301
|
1.68
|
2.015
|
2.414
|
2.692
|
3.286
|
3.526
|
|
46
|
1.3
|
1.679
|
2.013
|
2.41
|
2.687
|
3.277
|
3.515
|
|
48
|
1.299
|
1.677
|
2.011
|
2.407
|
2.682
|
3.269
|
3.505
|
|
50
|
1.299
|
1.676
|
2.009
|
2.403
|
2.678
|
3.261
|
3.496
|
|
55
|
1.297
|
1.673
|
2.004
|
2.396
|
2.668
|
3.245
|
3.476
|
|
60
|
1.296
|
1.671
|
2
|
2.39
|
2.66
|
3.232
|
3.46
|
|
65
|
1.295
|
1.669
|
1.997
|
2.385
|
2.654
|
3.22
|
3.447
|
|
70
|
1.294
|
1.667
|
1.994
|
2.381
|
2.648
|
3.211
|
3.435
|
|
80
|
1.292
|
1.664
|
1.99
|
2.374
|
2.639
|
3.195
|
3.416
|
|
100
|
1.29
|
1.66
|
1.984
|
2.364
|
2.626
|
3.174
|
3.39
|
|
150
|
1.287
|
1.655
|
1.976
|
2.351
|
2.609
|
3.145
|
3.357
|
|
200
|
1.286
|
1.653
|
1.972
|
2.345
|
2.601
|
3.131
|
3.34
|
|
