Scientific inquiry: finding answers to empirical questions: questions that can be answered by observing the world and measuring aspects of it. Scientific method: systematic procedure of observing and measuring phenomena to answer questions about what happens, when it happens, what causes it, and why. The scientific method depends on theories, hypotheses, and research. Hypothesis: specific prediction of what should be observed in the world if a theory is correct. Research: scientific process that involves the systematic and careful collection of data. Replication: repetition of an experiment to confirm the results. Three main types of designs: descriptive, correlational and experimental. > designs differ in the extent to which the researcher has control over the variables in the study and therefore extent to which conclusions can be made about causation. Variable: something in the world that can be measured and that can vary. Researchers must define variables precisely; identify and quantify variables so they can be measured.