Research design is determined by the sensitivity of the test, size of test sample, population you wish to generalize to, and funding limitations. If you need extra time to determine an outcome, your research advisor will tell you. Much of the variable in this is dependent on research design; for example, if you are researching the average longevity of light bulbs, you have to test about 30 to 40 bulbs for hundreds of hours, until more than half fail. If you are testing people for reaction times to visual stimuli, 30 subjects can be tested in a matter of days.
