<P> Hypothesis testing works by collecting data and measuring how likely the particular set of data is, assuming the null hypothesis is true, when the study is on a randomly selected representative sample . The null hypothesis assumes no relationship between variables in the population from which the sample is selected . </P> <P> If the data - set of a randomly selected representative sample is very unlikely relative to the null hypothesis (defined as being part of a class of sets of data that only rarely will be observed), the experimenter rejects the null hypothesis concluding it (probably) is false . This class of data - sets is usually specified via a test statistic which is designed to measure the extent of apparent departure from the null hypothesis . The procedure works by assessing whether the observed departure measured by the test statistic is larger than a value defined so that the probability of occurrence of a more extreme value is small under the null hypothesis (usually in less than either 5% or 1% of similar data - sets in which the null hypothesis does hold). </P> <P> If the data do not contradict the null hypothesis, then only a weak conclusion can be made: namely, that the observed data set provides no strong evidence against the null hypothesis . In this case, because the null hypothesis could be true or false, in some contexts this is interpreted as meaning that the data give insufficient evidence to make any conclusion; in other contexts it is interpreted as meaning that there is no evidence to support changing from a currently useful regime to a different one . </P> <P> For instance, a certain drug may reduce the chance of having a heart attack . Possible null hypotheses are "this drug does not reduce the chances of having a heart attack" or "this drug has no effect on the chances of having a heart attack". The test of the hypothesis consists of administering the drug to half of the people in a study group as a controlled experiment . If the data show a statistically significant change in the people receiving the drug, the null hypothesis is rejected . </P>

What is the meaning of the null hypothesis being rejected
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