a bug with Student t-value??

Hello, every one,

Using the qt() function in R, I got a different Student t-value
with the Student t table.
e.g. the return value of function qt(0.95,9) is 1.833, while in
table it is 2.262.

I do not know why the difference exists. I guess it may be a bug
in R.
-- 

Not at all. The reason is that your table gives the t-value for a
two-sided test (with equal tails), i.e. 0.025 in each tail.
The function qt() in R returns the t-value for a one-sided test,
i.e. 0.05 in the (by default) upper tail. Compare:

  qt(0.95,9)
# [1] 1.833113
  qt(0.975,9)
# [1] 2.262157

The second value agrees with your table. Many printed tables give
the two-sided values, rather than the one-sided.

Hoping this helps,
Ted.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
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Date: 07-Nov-09                                       Time: 09:55:50
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