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Type I Error Rate (α) Calculator

The probability of rejecting the null hypothesis when it is actually true.

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Alpha Level

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Overview

The Type I Error Rate (a) represents the probability of a 'false positive,' which occurs when a researcher incorrectly rejects a true null hypothesis. It is the pre-defined significance threshold that determines whether an observed effect is considered statistically significant or merely the result of random variation.

Symbols

Variables

\alpha = Alpha Level

Alpha Level

Apply it well

When To Use

When to use: Establish the alpha level before data collection to set the threshold for rejecting the null hypothesis. It is used in all frequentist inferential statistics, such as t-tests and regressions, to quantify the risk of reporting a non-existent effect.

Why it matters: Controlling the Type I error rate is vital for scientific integrity, as it prevents the proliferation of false claims in academic literature. In clinical settings, a high alpha could lead to the adoption of ineffective or even harmful psychological interventions.

Avoid these traps

Common Mistakes

  • Confusing Type I (False Positive) with Type II (False Negative).

One free problem

Practice Problem

A social psychologist is designing an experiment to test a new educational intervention. They decide that they are willing to accept a 5% risk of incorrectly rejecting the null hypothesis. What is the value of the Type I Error Rate (a) for this study?

Alpha Level0.05

Solve for:

Hint: Convert the percentage to a decimal by dividing by 100.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Field, A. (2018). Discovering Statistics Using IBM SPSS Statistics (5th ed.). SAGE Publications.
  2. Shaughnessy, J. J., Zechmeister, E. B., & Zechmeister, J. S. (2015). Research Methods in Psychology (10th ed.). McGraw-Hill Education.
  3. Wikipedia: Type I and Type II errors
  4. Discovering Statistics Using IBM SPSS Statistics by Andy Field
  5. Statistics for Psychology by Arthur Aron, Elaine Aron, and Elliot Coups
  6. American Psychological Association (APA) Publication Manual
  7. Howell, D. C. (2013). Statistical Methods for Psychology (8th ed.). Wadsworth Cengage Learning.
  8. IUPAC Gold Book: Type I error