Re: F-test questions (freshman level)

I recently did some ANOVA work on a set of data with
four columns of 6
elements each. Even I could figure out that the
degrees of freedom were
3 and 20. Then I looked up the table and chose n1 as
20 and n2 as 3. I
was shocked by the answer, which suggested that the
differences were
coincidental. (The table sure _looked_ like the
columns were different
-- only one cell of the first three columns had a
value as great as the
mean of the fourth.)

Then, I looked again and decided that I had used the
wrong numbers.
With n1 = 3
and n2 = 20, the .01 confidence value would be 4.9.
(I'm not sure that
"n1" and "n2" are universally differentitated the way
the book does.)

Two questions. The first, of practical importance, is
whether this is
the right way of doing it.

The second, merely curiosity, is _how_ a value of F
with n1 = 20 and n2
= 3 could be used. If you have twenty-one columns,
and only two values
in each column, then you'd have n2 = 21 -- wouldn't
you?

Thanks for any help. (I shuld have taken a course in
stat back in the
'60s; I was too pure a math student.)

Frank


First, a correction regarding terminlogy. The .01 entry that you obtained from the table is called the critical value, not the confidence value.

4.9 is indeed the correct value. n1 and n2 are called the degrees of freedom. For the F distribution, there are two of them.

One way in which n1 = 20 and n2 = 3 can be obtained is when you have 21 columns. The first column has 4 rows, while the remaining columns each have one row.

Jack
.

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