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Statistics For Dummies, 2nd Edition
The t-Table
Table A-2 shows right-tail probabilities for selected t-distributions
(see Chapter 10 for more on the t-distribution).
Follow these steps to use Table A-2 to find right-tail probabilities and
p-values for hypothesis tests involving t (see Chapter 15):
1. Find the t-value for which you want the right-tail probability (call it t),
and find the sample size (for example, n).
2. Find the row corresponding to the degrees of freedom (df ) for your

problem (for example, n – 1). Go across that row to find the two t-val-
ues between which your t falls.

For example, if your t is 1.60 and your n is 7, you look in the row for
df = 7 – 1 = 6. Across that row you find your t lies between t-values 1.44
and 1.94.
3. Go to the top of the columns containing the two t-values from Step 2.
The right-tail (greater-than) probability for your t-value is somewhere
between the two values at the top of these columns. For example, your
t = 1.60 is between t-values 1.44 and 1.94 (df = 6); so the right tail prob-
ability for your t is between 0.10 (column heading for t = 1.44); and 0.05
(column heading for t = 1.94).
The row near the bottom with Z in the df column gives right-tail (greater-than)
probabilities from the Z-distribution (Chapter 10 shows Z’s relationship
with t).
Use Table A-2 to find t*-values (critical values) for a confidence interval
involving t (see Chapter 13):
1. Determine the confidence level you need (as a percentage).
2. Determine the sample size (for example, n).
3. Look at the bottom row of the table where the percentages are shown.
Find your % confidence level there.
4. Intersect this column with the row representing your degrees of free-
dom (df). This is the t-value you need for your confidence interval.
For example, a 95% confidence interval with df=6 has t*=2.45. (Find 95%
on the last line and go up to row 6.)

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