Experiments is the step in the scientific method that arbitrates between competing scientific models or hypotheses. Experimentation is also used to test existing theories or new hypotheses in order to support them or disprove them. An experiment or test can be carried out using the scientific method to answer a question or investigate a problem. First an observation is made. Then a question is asked, or a problem arises. Next, a hypothesis is formed. Then experiment is used to test that hypothesis. The results are analyzed, a conclusion is drawn, sometimes a theory is formed, and results are communicated through research papers.
A good experiment usually tests a hypothesis. However, an experiment may also test a question or test previous results.
* Replication of results is "a standard procedure in the validation of any scientific discovery."
* "Science was long protected from scientific fraud by a built-in safety mechanism: to be generally accepted, experiments must be repeatable by others." [http://www.time.com/time/magazine/article/0,9171,953258-2,00.html
It is important that one knows all factors in an experiment. It is also important that the results are as accurate as possible. If an experiment is carefully conducted, the results usually either support or disprove the hypothesis. An experiment can never "prove" a hypothesis, it can only add support. However, one repeatable experiment that provides a counterexample can disprove a theory or hypothesis. An experiment must also control the possible confounding -- any factors that would mar the accuracy or repeatability of the experiment or the ability to interpret the results.
* "... the results of an experiment can never uniquely identify the explanation. They can only split the range of available models into two groups, those that are consistent with the results and those that aren't."
Experiments are not the only method that scientists use to test hypotheses. An experiment usually refers to observations in which conditions are artificially controlled and manipulated by the experimenter to eliminate extraneous factors, often in a Laboratory. Information about nature is also gathered and hypotheses tested in observational study and Field study, which are observations of phenomena in a natural setting, without control by the experimenter.