This document defines key concepts in research methods including concepts, constructs, variables, and different types of variables. It explains that concepts are categories or generalizations formed from specific instances that share common characteristics. Constructs are complex concepts that cannot be directly observed but are defined by specific indicators. Variables can assume different values and can be categorized as attribute or active, continuous or discrete, and dependent or independent. The document also outlines different measurement scales for data including nominal, ordinal, interval, and ratio scales.