# Significance Level

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A Significance Level is the probability of committing a Type I error.

**AKA:**Type I Error Rate, α.**Context:**- It can also be defined as the probability of rejecting the null hypothesis given that is true, i.e. [math]\displaystyle{ P\big( \mbox{reject } H_0 \big| H_0 \mbox{ is true} \big) }[/math].
- It can be defined as [math]\displaystyle{ \alpha=1 - \frac{\text{confidence level}}{100} }[/math]

**Example(s):**- A False Positive Error Rate.
- Given a confidence level of [math]\displaystyle{ 95\% }[/math] the significance level is [math]\displaystyle{ \alpha=1-(95/100)=0.05 }[/math]

**Counter-Example(s):****See:**Region of Rejection, Null Hypothesis, Hypothesis Test Acceptance Region, Statistical Hypothesis Testing Task.

## References

### 2017a

- (Wikipedia, 2017) ⇒ http://en.wikipedia.org/wiki/Type_I_and_type_II_errors#Type_I_error
- A
**type I error**occurs when the null hypothesis (*H*_{0}) is true, but is rejected. It is**asserting something that is absent**, a**false hit**. A type I error may be likened to a so-called*false positive*(a result that indicates that a given condition is present when it actually is not present).

- A

- The type I error rate or
**significance level**is the probability of rejecting the null hypothesis given that it is true.^{[1]}^{[2]}It is denoted by the Greek letter α (alpha) and is also called the alpha level. Often, the significance level is set to 0.05 (5%), implying that it is acceptable to have a 5% probability of incorrectly rejecting the null hypothesis.^{[1]}

- The type I error rate or

### 2017b

- (Stat Treak, 2017) ⇒ http://stattrek.com/statistics/dictionary.aspx?definition=P-value
*Retrieved: 2017-03-07*- A Type I error occurs when the researcher rejects a null hypothesis when it is true. The probability of committing a Type I error is called the significance level, and is often denoted by α.

- ↑
^{1.0}^{1.1}Lindenmayer, David; Burgman, Mark A. (2005). "Monitoring, assessment and indicators".*Practical Conservation Biology*(PAP/CDR ed.). Collingwood, Victoria, Australia: CSIRO Publishing. pp. 401–424. ISBN 0-643-09089-4. - ↑ Schlotzhauer, Sandra (2007).
*Elementary Statistics Using JMP (SAS Press)*(1 ed.). Cary, NC: SAS Institute. pp. 166–423. ISBN 1-599-94375-1.