Null hypothesis: The statement being tested in a statistical test is called the null hypothesis H0. Usually the null hypothesis is a statement of "no effect" or "no difference."Alternative hypothesis: The claim about a population that we are trying to find evidence for is the alternative hypothesis, written Ha. The alternative hypothesis is one-sided if it states that a parameter is larger than or smaller than the null hypothesis value. It is two-sided if it states that the parameter is different from the null value (it could be either smaller or larger).We abbreviate the null hypothesis as H0 and the alternative hypothesis as Ha. Hypotheses always refer to a population, not to a particular outcome. Be sure to state H0 and Ha in terms of population parameters. Because Ha expresses the effect that we hope to find evidence for, it is sometimes easier to begin by stating Ha and then set up H0 as the statement that the hoped-for effect is not present.
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