![]() ![]() The choice of significance level at which you reject H 0 is arbitrary. It does NOT imply a "meaningful" or "important" difference that is for you to decide when considering the real-world relevance of your result. accept that your sample gives reasonable evidence to support the alternative hypothesis. If your P value is less than the chosen significance level then you reject the null hypothesis i.e. For example, question is "is there a significant (not due to chance) difference in blood pressures between groups A and B if we give group A the test drug and group B a sugar pill?" and alternative hypothesis is " there is a difference in blood pressures between groups A and B if we give group A the test drug and group B a sugar pill". The alternative hypothesis (H 1) is the opposite of the null hypothesis in plain language terms this is usually the hypothesis you set out to investigate. ![]() The term significance level (alpha) is used to refer to a pre-chosen probability and the term "P value" is used to indicate a probability that you calculate after a given study. This situation is unusual if you are in any doubt then use a two sided P value. The only situation in which you should use a one sided P value is when a large change in an unexpected direction would have absolutely no relevance to your study. ![]() Define a null hypothesis for each study question clearly before the start of your study. no difference between blood pressures in group A and group B. The null hypothesis is usually an hypothesis of "no difference" e.g. P is also described in terms of rejecting H 0 when it is actually true, however, it is not a direct probability of this state. The P value, or calculated probability, is the probability of finding the observed, or more extreme, results when the null hypothesis (H 0 ) of a study question is true – the definition of ‘extreme’ depends on how the hypothesis is being tested. ![]()
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