An hypothesis is a conclusion drawn before all of the facts are established and tentatively accepted as a basis for further investigation.

A conclusion is the final operation in the scientific method. It is a decision made about the validity of the hypothesis on the basis of experimental evidence. Observation is the first operation in the scientific method. Observation is the noting of a specific phenomenon leading to the formulation of a hypothesis. Perception is the organization, identification, and interpretation of sensory information. An assumption is an idea that is not subjected to logical study.

In an experiment, the dependent variable is changed by changes to the independent variable; because this study examines how differences in smoking habits affect blood pressure, the number/frequency of cigarettes smoked is the study's independent variable and the subjects' blood pressure is the study's dependent variable.