Validity in Experimentation Internal validity refers to whether the manipulation of the independent variables or treatments actually caused the observed effects on the dependent variables. Įxperimental Design An experimental design is a set of procedures specifying the test units and how these units are to be divided into homogeneous subsamples, what independent variables or treatments are to be manipulated, what dependent variables are to be measured, and how the extraneous variables are to be controlled. Extraneous variables are all variables other than the independent variables that affect the response of the test units, e.g., store size, store location, and competitive effort. Dependent variables are the variables which measure the effect of the independent variables on the test units, e.g., sales, profits, and market shares. Test units are individuals, organizations, or other entities whose response to the independent variables or treatments is being examined, e.g., consumers or stores. Purchase of Fashion Clothing By Income and Education Low Income Purchase High Low High Low Education 200 (100%) 300 (100%) 300 200 122 (61%) 171 (57%) 78 (39%) 129 (43%) High Income Purchase High High Low Low 241 (80%) 151 (76%) 59 (20%) 49 (24%) Educationĭefinitions and Concepts Independent variables are variables or alternatives that are manipulated and whose effects are measured and compared, e.g., price levels. Įvidence of Concomitant Variation between Purchase of Fashion Clothing and Education High High Low 363 (73%) 137 (27%) 322 (64%) 178 (36%) Purchase of Fashion Clothing, Y 500 (100%) 500 (100%) Low Education, X The absence of other possible causal factors means that the factor or variable being investigated should be the only possible causal explanation. The time order of occurrence condition states that the causing event must occur either before or simultaneously with the effect it cannot occur afterwards. _ Ĭonditions for Causality Concomitant variation is the extent to which a cause, X, and an effect, Y, occur together or vary together in the way predicted by the hypothesis under consideration. At best, we can infer that X is a cause of Y. It is possible to prove We can never prove that X is a that X is a cause of Y. X must always lead to Y The occurrence of X makes the ( X is a deterministic occurrence of Y more probable cause of Y ).
X is only one of a number of possible causes of Y. _ Ordinary Meaning Scientific Meaning _ X is the only cause of Y. Non-experimental Designs 16) Limitations of Experimentation 17) Summary 18) Key Terms and Concepts Ĭoncept of Causality A statement such as ' X causes Y ' will have the following meaning to an ordinary person and to a scientist. Chapter Outline 1) Overview 2) Concept of Causality 3) Conditions for Causality 4) Definition of Concepts 5) Definition of Symbols 6) Validity in Experimentation 7) Extraneous Variables 8) Controlling Extraneous Variables 9) A Classification of Experimental Designs 10) Pre-experimental Designs 11) True Experimental Designs Ĭhapter Outline 12) Quasi Experimental Designs 13) Statistical Designs 14) Laboratory vs.
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