The F distributions are a family of distributions with two parameters, the degrees of freedom of the sample variances in the numerator and denominator of the F statistic. The numerator degrees of freedom are always given first. The F distributions are not symmetric but are right skewed. The density curve figure illustrates the shape. Because sample variances cannot be negative, the F statistic takes only positive values and the F distribution has no probability below zero.The peak of the F density curve is near one; values far from one in either direction provide evidence against the hypothesis of equal standard deviations.
Table of the Upper Percentage Points of the F distribution
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
15 |
||
1 |
.05 |
161 |
200 |
216 |
225 |
230 |
234 |
237 |
239 |
241 |
242 |
243 |
244 |
246 |
2 |
.05 |
18.51 |
19.00 |
19.16 |
19.25 |
19.39 |
19.33 |
19.36 |
19.37 |
19.38 |
19.39 |
19.4 |
19.4 |
19.4 |
3 |
.05 |
10.13 |
9.55 |
9.28 |
9.12 |
9.01 |
8.94 |
8.88 |
8.84 |
8.81 |
8.78 |
8.76 |
8.74 |
8.70 |
4 |
.05 |
7.71 |
6.94 |
6.59 |
6.39 |
6.26 |
6.16 |
6.09 |
6.04 |
6.00 |
5.96 |
5.93 |
5.91 |
5.86 |
5 |
.05 |
6.61 |
5.79 |
5.41 |
5.19 |
5.05 |
4.95 |
4.88 |
4.82 |
4.78 |
4.74 |
4.70 |
4.68 |
4.62 |
6 |
.05 |
5.99 |
5.14 |
4.76 |
4.53 |
4.39 |
4.28 |
4.21 |
4.15 |
4.10 |
4.06 |
4.03 |
4.00 |
3.94 |
7 |
.05 |
5.59 |
4.74 |
4.35 |
4.12 |
3.97 |
3.87 |
3.79 |
3.73 |
3.68 |
3.63 |
3.60 |
3.57 |
3.51 |
8 |
.05 |
5.32 |
4.46 |
4.07 |
3.84 |
3.69 |
3.58 |
3.50 |
3.44 |
3.39 |
3.34 |
3.31 |
3.28 |
3.22 |
9 |
.05 |
5.12 |
4.26 |
3.86 |
3.63 |
3.48 |
3.37 |
3.29 |
3.23 |
3.18 |
3.14 |
3.10 |
3.07 |
3.01 |
10 |
.05 |
4.96 |
4.10 |
3.71 |
3.48 |
3.33 |
3.22 |
3.14 |
3.07 |
3.02 |
2.97 |
2.94 |
2.91 |
2.85 |
20 |
.05 |
4.30 |
3.44 |
3.05 |
2.82 |
2.66 |
2.55 |
2.46 |
2.40 |
2.34 |
2.30 |
2.31 |
2.28 |
2.20 |
30 |
.05 |
4.17 |
3.32 |
2.92 |
2.69 |
2.53 |
2.42 |
2.33 |
2.27 |
2.21 |
2.16 |
2.12 |
2.09 |
2.01 |
40 |
.05 |
4.08 |
3.23 |
2.84 |
2.61 |
2.45 |
2.34 |
2.25 |
2.18 |
2.12 |
2.08 |
2.04 |
2.00 |
1.92 |
50 |
.05 |
4.03 |
3.18 |
2.79 |
2.56 |
2.40 |
2.29 |
2.20 |
2.13 |
2.07 |
2.03 |
1.98 |
1.95 |
1.87 |
60 |
.05 |
4.00 |
3.15 |
2.76 |
2.53 |
2.37 |
2.25 |
2.17 |
2.10 |
2.04 |
1.99 |
1.95 |
1.92 |
1.84 |
70 |
.05 |
3.98 |
3.13 |
2.74 |
2.50 |
2.35 |
2.23 |
2.14 |
2.07 |
2.01 |
1.97 |
1.93 |
1.89 |
1.82 |
80 |
.05 |
3.96 |
3.11 |
2.72 |
2.48 |
2.33 |
2.21 |
2.12 |
2.05 |
1.99 |
1.95 |
1.91 |
1.88 |
1.80 |
100 |
.05 |
3.94 |
3.09 |
2.70 |
2.46 |
2.31 |
2.19 |
2.10 |
2.03 |
1.97 |
1.93 |
1.88 |
1.85 |
1.77 |
200 |
.05 |
3.89 |
3.04 |
2.65 |
2.42 |
2.26 |
2.14 |
2.06 |
1.98 |
1.93 |
1.88 |
1.83 |
1.80 |
1.72 |
400 |
.05 |
3.86 |
3.02 |
2.62 |
2.39 |
2.23 |
2.12 |
2.03 |
1.96 |
1.90 |
1.85 |
1.81 |
1.78 |
1.70 |
1000 |
.05 |
3.85 |
3.00 |
2.61 |
2.38 |
2.22 |
2.11 |
2.02 |
1.95 |
1.89 |
1.84 |
1.80 |
1.76 |
1.68 |
Inf |
.05 |
3.85 |
2.99 |
2.60 |
2.37 |
2.21 |
2.09 |
2.01 |
1.94 |
1.88 |
1.83 |
1.79 |
1.75 |
1.66 |