# statistics analysis and interpretation of research results type i and type ii errors 1

Type I and Type II Errors

Statisticians and researchers are human, and therefore, make mistakes in the conduct of their research. Type I and Type II errors are important to consider as they have real-world implications. A Type I error refers to rejecting a null hypothesis when it is true, while a Type II error results from failing to reject a null hypothesis when it is false. The following hypothetical situation illustrates these errors and the null hypothesis:

A forensic psychologist must decide whether to allow John Hinckley, Jr. to go to his parents’ house on a weekend pass. Mr. Hinckley, as you recall, attempted to assassinate President Reagan at the Washington Hilton in 1981, just to impress actress Jody Foster with whom he was obsessed. Mr. Hinckley has been writing letters to Miss Foster as recently as last month. The letters were found under his mattress during a routine inspection of his room at St. Elizabethâ€™s Hospital. The hospital has convened a panel of seven mental health professionals, all of whom work at the hospital and with Mr. Hinckley. The votes are in: Three say let him go visit his parents and three vote to deny his weekend pass request. What should the forensic psychologist decide? The null hypothesis in this case would be that it is safe to send him home for the weekend. If he is denied the visit when in reality he would not have caused any problems, a Type I error (also called a false positive) would have been made. It was determined that he would be dangerous when he would not have been. A Type II error (or a false negative) would result if it was determined that he would not be violent and he was released, and he ended up assaulting someone on his weekend pass. In that case, it was believed that nothing would happen and it did.

Forensic psychology research also may exhibit Type I and Type II errors, use the following resources:

• Review Chapter 8 in your course text, Research Methods for the Behavioral Sciences. Pay particular attention to the difference between Type I and Type II errors.
• Review the web article, â€œ Type I and Type II Errorsâ€”Making Mistakes in the Justice System.â€ Pay close attention to the descriptions and examples of Type I and Type II errors. Article: Intuitor. (2001). Type I and Type II errorsâ€”making mistakes in the justice system. Retrieved from http://www.intuitor.com/statistics/T1T2Errors.html
• Select and review a research article that addresses a forensic psychology issue or takes place in a forensic setting, and that reports or discusses a Type I or Type II error.
• Think about the possible consequences to the research study of making each type of error.
• Consider whether the resulting consequences of making each type of error would be tolerable or not and why.

With these thoughts in mind w