Null Hypotheses| Alternative Hypotheses|Hypothesis Test|Significance Level|two tailed |one tailed|

9.1 The Nature of Hypothesis Testing

Over the years, however, null hypothesis has come to mean simply a hypothesis to be tested.

Null Hypothesis:

H0: μ = μ0,

where μ0 is some number

Alternative Hypothesis:

two tailed 实例：

one tailed 实例：

评判标准：

Type I and Type II Errors：

Significance Level

所以需要balancing

In other words, if we do not reject the null hypothesis, we conclude only that the data do not provide sufficient evidence to support the alternative hypothesis; we do not conclude that the data provide sufficient evidence to support the null hypothesis

即，reject or not reject 取决于是否满足备择假设，如果满足备择假设则reject；如果不满足备择假设则 not reject

When the null hypothesis is rejected in a hypothesis test performed at the significance level α, we frequently express that fact with the phrase “the test results are statistically significant at the α level.” Similarly, when the null hypothesis is not rejected in a hypothesis test performed at the significance level α, we often express that fact with the phrase “the test results are not statistically significant at the α level.”