3. Criteria for Establishing Causal Relationships Concomitant variation Temporal ordering of variables Control over other possible causal factors

7. Threats to Internal Validity

25. Experiment A research investigation in which conditions are controlled One independent variable is manipulated (sometimes more than one) Its effect on a dependent variable is measured To test a hypothesis

26. Basic Issues of Experimental Design Manipulation of the Independent Variable Selection of Dependent Variable Assignment of Subjects (or other Test Units) Control Over Extraneous Variables

27. The experimenter has some degree of control over the independent variable. The variable is independent because its value can be manipulated by the experimenter to whatever he or she wishes it to be.

28. Experiment Treatment Alternative manipulations of the independent variable being investigated

29. Independent Variable The experimenter controls independent variable. The variable’s value can be manipulated by the experimenters to whatever they wish it to be.

30. Manipulation of Independent Variable Classificatory vs. continuous variables Experimental and control groups Treatment levels More than one independent variable

31. Experimental Treatments The alternative manipulations of the independent variable being investigated

32. Dependent Variable Its value is expected to be dependent on the experimenter’s manipulation Criterion or standard by which the results are judged

33. Dependent Variable Selection –e.g... sales volume, awareness, recall, Measurement

34. Test Units Subjects or entities whose response to the experimental treatment are measured or observed.

35. Two Types of Experimental Error Constant errors Random errors

36. Field versus Laboratory Experiments

37. Controlling Extraneous Variables Elimination of extraneous variables Constancy of conditions Order of presentation Blinding Random assignment

38. How May an Experimenter control for Extraneous Variation? Eliminate Extraneous Variables Hold Conditions Constant Randomization Matching Subjects

39. Demand Characteristics Experimental procedures that intentionally hint to subjects something about the experimenter’s hypothesis

40. Demand Characteristics Guinea pig effect Hawthorne effect

41. Field vs. Laboratory Experiment

42. Laboratory ExperimentField Experiment Artificial-Low Realism Few Extraneous Variables High control Low Cost Short Duration Subjects Aware of Participation Natural-High Realism Many Extraneous Variables Low control High Cost Long Duration Subjects Unaware of Participation

43. Control Groups Isolate extraneous variation

44. When does an Experiment have Internal Validity? Internal Validity - The ability of an experiment to answer the question whether the experimental treatment was the sole cause of changes in a dependent variable Did the manipulation do what it was supposed to do?

45. Factors Influencing Internal Validity History Maturation Testing Instrumentation Selection Mortality

46. Isolating Extraneous Variation with a Control Group History Effects Maturation Effects Mortality Effects

47. Type of Extraneous VariableExample History - Specific events in the environment between the Before and After measurement that are beyond the experimenter’s control Maturation - Subjects change during the course of the experiment Testing - The Before measure alerts or sensitizes subject to nature of experiment or second measure. A major employer closes its plant in test market area Subjects become tired Questionnaire about the traditional role of women triggers enhanced awareness of women in an experiment.

48. Instrument - Changes in instrument result in response bias Selection - Sample selection error because of differential selection comparison groups Mortality - Sample attrition; some subjects withdraw from experiment New questions about women are interpreted differently from earlier questions. Control group and experimental group is self-selected group based on preference for soft drinks Subjects in one group of a hair dying study marry rich widows and move to Florida

49. Increasing Internal Validity Control group Random assignment Pretesting and posttesting Posttest only