Null Hypothesis

What is the null hypothesis? How do researchers determine whether or not to reject the null hypothesis? Why is it said that hypothesis testing involves double negative logic?

Our text defines a null hypothesis as a statement about a relation between the two populations in a study (Aron, Aron, & Coups, 2009).  This hypothesis is the opposite of the research hypothesis. Researchers use z scores to determine whether to reject the null hypothesis. The actual samples’ z scores are compared to the cutoff z score. If the actual score exceeds the cutoff score, then the null hypothesis is rejected. Hypothesis testing involves double negative logic because the null hypothesis is never accepted only rejected. If research does not reject the null hypothesis, it is worded as “failure to reject the null hypothesis”. One never says they have accepted the null hypothesis.

Aron, A., Aron, E. N., & Coups, E. J. (2009). Statistics for psychology (5th ed). Upper Saddle River, NJ: Pearson/Prentice Hall.

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