Scientific methodology is empirical. This means that it focuses on events or information that can be directly observed. Scientists conduct experiments to measure effects that can be concretely assessed instead of relying on their own thinking or reasoning to come to an answer. In addition, they make their observations and conclusions in a methodical, step-by-step manner instead of haphazardly.
The scientific method relies on hypotheses to develop new knowledge in a field. A scientist comes up with a hypothesis, or educated guess as to what will happen, based on prior research done by other scientists. She then conducts an experiment to test the question that the hypothesis poses. In science, a hypothesis can be disproved by experiment, but never proven. A scientific hypothesis should be precise, but simple, and must be able to be tested by an experiment. A group of related hypothesis that time after time appear true, through experiment, develop into a theory but can still be questioned.
Scientists test their hypotheses by performing experiments. Experiments must be conducted and written in such a way that later researchers can accurately do the same experiment over again. This is called replication and is necessary because one experiment is not enough to demonstrate the existence of a certain phenomenon or relationship.
These experiments revolve around measurable amounts or characteristics called "variables." A scientific researcher changes the independent variable and then measures the difference, or lack thereof, that this causes in the dependent variable. For instance, he might change the amount of sunlight available to different plants (independent variable) and then measure the heights of these plants (dependent variable). In a laboratory setting, a scientist tries to eliminate all other potential variables by keeping the environment as consistent as possible. That way, he can more accurately say that a change in the independent variable is related to a change in the dependent variable.
Sometimes curiosity drives scientists to design new experiments or test new hypotheses. This is called "pure" research or "basic" research because it is conducted solely to expand the body of scientific knowledge. On the other hand, scientists carry out "applied" research to discover new technologies or concepts that can be used in the field. For instance, applied research supplies governments, pharmaceuticals, therapists, schools and companies with ever-evolving products and techniques.
Scientific methodology requires that researchers work objectively. This means that a scientist cannot let her personal opinions or beliefs influence her work. She must not let a desire for experiments to turn out a certain way impact the manner in which she reads research, formulates hypotheses, makes observations and analyzes her results. She should always be skeptical and open-minded when considering evidence.