Quick Answer. In some rare cases, excessive stress causes bleeding between periods. It is more common that another condition is responsible, such as pregnancy, polycystic ovary syndrome, infection, pelvic inflammatory disease or side effects of medication, according to WebMD.
Using the scientific method, you can repeat the experiment to find out for yourself whether or not the other researcher's assertions are true. This is a key factor that separates science from dogma! The other important part of scientific research is that a hypothesis must be falsifiable. A falsifiable hypothesis or theory is one where an experiment or another discovery can prove it to be wrong, untrue, and false.
The usefulness of scientific knowledge is limited if that knowledge is not communicated to other people. Scientists often communicate their research results in three general ways. One is to publish their results in peer-reviewed journals that can be ready by other scientists. Two is to present their results at national and international conferences where other scientists can listen to presentations.