In designing experiments, there is an additional issue to consider: the size of each of our groups. The dependent variable is the presence or absence of headache following treatment. In our example of the headache medicine, the independent variable is the type of medicine (new medicine, no medicine, placebo, or medicine known to be effective). ![]() It is considered “dependent” because the expectation is that it depends on the variable that was changed. The dependent variable is the effect that is being measured. It is considered “independent” because the researchers could choose any variable they wish. An independent variable is the manipulation performed on the test group by the researchers. When performing experiments, researchers manipulate the test group differently from the control groups. Each of these models is an alternative hypothesis, one or more of which might be correct. Our question might be: How does the protein repress the expression of the gene? In this case, we might come up with several models-the protein might block transcription, it might block translation, or it might interfere with the function of the protein product of the gene. Let’s say for example that we discover a protein that represses the expression of a gene. This may be the case when researchers consider different explanations of their data. Sometimes, we formulate several alternative hypotheses to answer a single question. When a null hypothesis is rejected, the hypothesis gains support. ![]() Hypotheses are never proven, but it is possible based on statistical analysis to reject a hypothesis. When an experiment predicts a specific effect, as in the case of the new medicine, it is typical to also state a null hypothesis, which predicts no effect. The answer has to wait until we conduct the experiment and look at the data. If we went into the experiment with no expectation at all, it would be unclear what to measure.Ī hypothesis is considered tentative because we don’t know what the answer is. For example, we might observe that the chemical structure of the medicine is similar to other drugs that we already know are used to treat headaches. This hypothesis is not just a hunch-it is based on previous observations or experiments. We design a new medicine and hypothesize that it can be used to treat headaches. ![]() Science, after all, is supposed to be unbiased, so why should you expect any particular result at all? The answer is that it helps to organize the experimental setup and interpretation of the data. This might at first seem counterintuitive. A hypothesis, as we saw in Chapter 1, is a tentative answer to the question, an expectation of what the results might be.
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