Editing Biostatistics (section)

=== Hypothesis definition ===

Once the aim of the study is defined, the possible answers to the research question can be proposed, transforming this question into a [[hypothesis]]. The main propose is called [[null hypothesis]] (H<sub>0</sub>) and is usually based on a permanent knowledge about the topic or an obvious occurrence of the phenomena, sustained by a deep literature review. We can say it is the standard expected answer for the data under the situation in [[Experiment|test]]. In general, H<sub>O</sub> assumes no association between treatments. On the other hand, the [[alternative hypothesis]] is the denial of H<sub>O</sub>. It assumes some degree of association between the treatment and the outcome. Although, the hypothesis is sustained by question research and its expected and unexpected answers.<ref name=":3" />

As an example, consider groups of similar animals (mice, for example) under two different diet systems. The research question would be: what is the best diet? In this case, H<sub>0</sub> would be that there is no difference between the two diets in mice [[metabolism]] (H<sub>0</sub>: μ<sub>1</sub> = μ<sub>2</sub>) and the [[alternative hypothesis]] would be that the diets have different effects over animals metabolism (H<sub>1</sub>: μ<sub>1</sub> ≠ μ<sub>2</sub>).

The [[hypothesis]] is defined by the researcher, according to his/her interests in answering the main question. Besides that, the [[alternative hypothesis]] can be more than one hypothesis. It can assume not only differences across observed parameters, but their degree of differences (''i.e.'' higher or shorter).