A test is reliable to the extent that whatever it measures, it measures it consistently. If I were to stand over a size and the range read 15 pounds, I would wonder. Imagine I were to step off the size and stand on it again, and again it read 15 pounds. The level is producing constant results. From a research point of view, the scale seems to be reliable because whatever it is calculating, it is calculating it regularly. Whether those constant results are valid is another question. However,..