Kerlinger, Fred N. (1973) Foundations of Behavioral Research. 2nd edition. Holt, Rinehart and Winston
Theory: "A set of interrelated constructs (concepts), definitions, and propositions that present a systematic view of phenomena specifying relations among variables, with the purpose of explaining and predicting the phenomena." (p.9)
Scientific Research: "Scientific research is systematic, controlled, empirical, and critical investigation of hypothetical propositions about the presumed relations among natural phenomena." (p. 11)
Hypothesis: "A conjectural statement, a tentative proposition, about the relation between two or more phenomena or variables." (p12).
"If X occurs ...then Y will follow."
Concept: "Expresses an abstraction formed by generalization from particulars. E.g. "weight expresses numerous observations of things that are more or less "heavy or "light." Others: Mass, energy, force, achievement, intelligence, motivation, extraversion., aggressiveness, conformity.
Construct: "is a concept with added meaning, deliberately and consciously invented or adopted for a special scientific purpose." (p.29) E.g. intelligence – used for a special purpose to relate to school achievement and to other variables of interest.
Operational definition: "assigns a meaning to a construct or a variable by specifying the activities or ‘operations’ necessary to measure it." (p,31)