This document discusses variables, hypotheses, and operationalization in experiments. It defines independent and dependent variables, and explains that the independent variable is manipulated while the dependent variable is measured. Extraneous variables that need to be controlled are also discussed. The document emphasizes that variables need to be operationalized by precisely defining how they will be manipulated or measured. It defines alternative and null hypotheses and explains that the null hypothesis states there will be no effect, while one-tailed and two-tailed alternative hypotheses predict effects in one or both directions. Examples of null and alternative hypotheses comparing men's and women's 100m run times are provided.