An operational hypothesis in a research experiment clearly defines what the variables of interest are and how the different variables are related to each other. The operational hypothesis should also define the relationship that is being measured and state how the measurement is occurring. It attempts to take an abstract idea and make it into a concrete, clearly defined method. It is used to inform readers how the experiment is going to measure the variables in a specific manner.
An operational hypothesis is more detailed than a general hypothesis. A general hypothesis for an example experiment would be that students who slept an hour extra the night before a test would perform better than those who slept the normal amount. An operational hypothesis would state that two groups of fifty high school students took an exam with one group having slept eight hours with the other group sleeping nine hours the night before in order to see if extra sleep improved test scores.