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# Hypotheses Testing

Rating

當你的 alternative hypotheses 是要證明不等於 null hypotheses，那麼就要用 two-tailed test 了。這情況下，不用考慮 alternative hypotheses 是大於或小於 null hypotheses。

而 one-tailed test 是要特別指明 alternative hypotheses 是大於或是小於 null hypotheses 時用。

例子：

one-tailed test

An engineer wants to investigate whether the new adjustment improves the mechanism. For negative μ, it is worsened.

在這個情況下

H0: μ = 0

H1: μ > 0

因我們是要研究是否有進步，所以若差了我們便不會計算在內。

two-tailed test

Whether the time is altered.

在這情況下，alternative hypotheses 是要證明time是有改變的。因此：

H0: μ = 0

H1: μ 不等於 0

值得留意的是，兩者的test statistics不同的。

例如two-tailed 的5% significant level，test statistics是1.96

而one-tailed的5% significant level是1.645。

Source(s): Myself~~~