Transact-SQL Cookbook

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

DF	Probabilities
	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