3/28/2023 0 Comments Typestatus 2 11.3Power is covered in detail in another section. The probability of correctly rejecting a false null hypothesis equals \(1-\beta\) and is called power. If the null hypothesis is false, then the probability of a Type II error is called \(\beta\) (beta). Contrast this with a Type I error in which the researcher erroneously concludes that the null hypothesis is false when, in fact, it is true.Ī Type II error can only occur if the null hypothesis is false. Instead, the researcher should consider the test inconclusive. Therefore, a researcher should not make the mistake of incorrectly concluding that the null hypothesis is true when a statistical test was not significant. Lack of significance does not support the conclusion that the null hypothesis is true. When a statistical test is not significant, it means that the data do not provide strong evidence that the null hypothesis is false. Unlike a Type I error, a Type II error is not really an error. This kind of error is called a Type II error. The second type of error that can be made in significance testing is failing to reject a false null hypothesis. If the null hypothesis is false, then it is impossible to make a Type I error. Instead, \(\alpha\) is the probability of a Type I error given that the null hypothesis is true. It might seem that \(\alpha\) is the probability of a Type I error. The Type I error rate is affected by the \(\alpha\) level: the lower the \(\alpha\) level, the lower the Type I error rate. Therefore, keep in mind that rejecting the null hypothesis is not an all-or-nothing decision. As discussed in the section on significance testing, it is better to interpret the probability value as an indication of the weight of evidence against the null hypothesis than as part of a decision rule for making a reject or do-not-reject decision. It is also called the significance level. The threshold for rejecting the null hypothesis is called the \(\alpha\) (alpha) level or simply \(\alpha\). Another convention, although slightly less common, is to reject the null hypothesis if the probability value is below \(0.01\). More generally, a Type I error occurs when a significance test results in the rejection of a true null hypothesis.īy one common convention, if the probability value is below \(0.05\), then the null hypothesis is rejected. This type of error is called a Type I error. If this is the case, then the conclusion that physicians intend to spend less time with obese patients is in error. Despite the low probability value, it is possible that the null hypothesis of no true difference between obese and average-weight patients is true and that the large difference between sample means occurred by chance. Therefore, the null hypothesis was rejected, and it was concluded that physicians intend to spend less time with obese patients. In the Physicians' Reactions case study, the probability value associated with the significance test is \(0.0057\). Explain why the null hypothesis should not be accepted when the effect is not significant.
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