The null hypothesis (H0) represents a theory that has been presented, either because it is believed to be true or because it is to be used as a basis for an argument. It is a statement that has not been proven. It is also important to realize that the null hypothesis is the statement of no difference. For example, in a clinical trial of a new drug, the null hypothesis might state that the new drug is no better, on average, than the current drug (in other words, the new drug exhibits the same behavior as the old drug). The null hypothesis (H0) and the alternative hypothesis (H1) can be stated as:

H0: There is no difference between the two drugs.
H1: There is a significant difference between the two drugs.

Special consideration is given to the null hypothesis. This is due to the fact that the null hypothesis relates to the statement being tested, whereas the alternative hypothesis relates to the statement to be accepted if and when the null hypothesis is rejected.

After testing is complete, the final conclusion is given in terms of the null hypothesis. The result is either "Reject H0 in favor of H1" or "Do not reject H0"; the conclusion is never "Reject H1" or "Accept H1."

If the conclusion is "Do not reject H0," this does not necessarily mean that the null hypothesis is true. It only suggests that there is no sufficient evidence against H0 in favor of H1. Rejecting the null hypothesis then suggests that the alternative hypothesis may be true.

NOTE: The null hypothesis essentially states that the given cases or items under consideration are statistically the same or exhibit the same behavior without any significant difference. The alternative hypothesis states that the given cases exhibit different behavior or that they have a statistically significant difference. Created by the ITS Training Program at CSULA for students.

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