Type I Error

Definition

A Type I error, also known as a false positive, occurs when the null hypothesis is true, but the test incorrectly rejects it. In other words, it is the error of concluding that a difference exists when, in reality, there is no actual difference between the populations or treatments being studied.

5 Must Know Facts For Your Next Test

1. A Type I error can occur in any hypothesis testing scenario, including tests for a single population mean, two population means, and population proportions.
2. The probability of making a Type I error is controlled by setting the significance level, which is typically chosen to be 0.05 or 5%.
3. Reducing the significance level decreases the chance of a Type I error but increases the chance of a Type II error, and vice versa.
4. The distribution used for hypothesis testing (e.g., $t$-distribution, $z$-distribution, $ extbackslash chi^2$-distribution) determines the critical value used to make the decision to reject or fail to reject the null hypothesis.
5. When the test statistic falls in the rejection region, the null hypothesis is rejected, and a Type I error may have occurred if the null hypothesis is true.

Review Questions

• Explain the concept of a Type I error and how it relates to the null hypothesis in hypothesis testing.
  • A Type I error occurs when the null hypothesis is true, but the test incorrectly rejects it. This means the test concludes there is a significant difference or relationship when, in reality, there is none. The null hypothesis represents the claim of no difference or no relationship, and a Type I error happens when the test falsely concludes that the null hypothesis is false. The probability of making a Type I error is controlled by the significance level, which is the maximum acceptable probability of rejecting the null hypothesis when it is true.
• Describe how the choice of significance level affects the risk of a Type I error and a Type II error.
  • The significance level, denoted as $\alpha$, is the probability of making a Type I error. Decreasing the significance level, such as from 0.05 to 0.01, reduces the chance of a Type I error but increases the chance of a Type II error (failing to reject the null hypothesis when it is false). Conversely, increasing the significance level raises the risk of a Type I error but lowers the risk of a Type II error. The researcher must balance the tradeoff between these two types of errors when selecting the appropriate significance level for the hypothesis test.
• Analyze how the distribution used for hypothesis testing impacts the decision to reject or fail to reject the null hypothesis and the potential for a Type I error.
  • The distribution used for hypothesis testing, such as the $t$-distribution, $z$-distribution, or $ extbackslash chi^2$-distribution, determines the critical value that is compared to the test statistic to make the decision to reject or fail to reject the null hypothesis. If the test statistic falls in the rejection region, the null hypothesis is rejected, and a Type I error may have occurred if the null hypothesis is true. The choice of distribution depends on factors like the population parameters known, the sample size, and the research question. Selecting the appropriate distribution is crucial, as it directly affects the likelihood of making a Type I error in the hypothesis testing process.

Related terms

Null Hypothesis: The null hypothesis, denoted as H₀, is a statement that there is no significant difference or relationship between the variables being studied.

Type II Error: A Type II error, or false negative, occurs when the null hypothesis is false, but the test fails to reject it. This means the test concludes there is no significant difference when, in fact, there is one.

Significance Level: The significance level, denoted as α, is the probability of making a Type I error. It is the maximum acceptable probability of rejecting the null hypothesis when it is true.