Yahoo 知識+ 將於 2021 年 5 月 4 日 (美國東岸時間) 停止服務。從 2021 年 4 月 20 日 (美國東岸時間) 起，Yahoo 知識+ 網站將轉為僅限瀏覽模式。其他 Yahoo 資產或服務，或你的 Yahoo 帳戶將不會有任何變更。你可以在此服務中心網頁進一步了解 Yahoo 知識+ 停止服務的事宜，以及了解如何下載你的資料。

ss5d14 發問於 科學及數學數學 · 1 十年前

# T-test critical value

+ 如果 degrees of freedom 係 200

### 2 個解答

• Andrew
Lv 6
1 十年前
最愛解答

It depends on whether you're doing one tail or two tails test. The critical value are usually found by looking up table because there is no closed form formula for computing the critical value.

In fact, the critical value is computed using the incomplete beta function. Numerical methods can be used to evaluate the definite integral numerically.

Microsoft excel provided the implementation for this. To compute the critical value, you can just use this formula.

=TINV(A1/100/(3-C1),B1)

Put this in cell A2. Put the significance value in A1, the degree of freedom in B1, and the one/two tail test (represented as 1 or 2) in C1, then you get the correct value for the critical value for the associated t-test.

Using excel, the critical values obtained are:

[5%, dof=150, one-tail] 2.264125047

[5%, dof=150, two-tails] 1.975905298

[5%, dof=200, one-tail] 2.25840314

[5%, dof=200, two-tails] 1.971896178

2008-08-26 00:05:33 補充：

Thanks for the correction from (victorng_email). I have a typo in the excel function.

It actually outputs the two tail test critical value.

2008-08-26 00:06:11 補充：

The real solution should be

5%, dof=150, one-tails = 1.65507550067786

5%, dof=150, two-tails = 1.97590529767365

5%, dof=200, one-tails = 1.65250810140191

5%, dof=200, two-tails = 1.97189617759775

Given by the formula:

=TINV(A2/100*(3-C2),B2)

資料來源： 從不抄襲。, 從不抄襲。
• 1 十年前

I have a little bit of reservation on Andrew's answer.

The critical value of a one-tailed test should not be greater than a two-tailed test [due to greater area on right hand side]

Here's figures obtained from R:

df=150: 1.655076 ; df=200: 1.652508