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Chapter 8 Experiments

Chapter 8 Experiments. The Classical Experiment. The most conventional type of experiment involves three major pairs of components: 1) independent and dependent variables 2) pre-testing and post-testing 3) experimental and control groups. Independent and dependent variables.

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Chapter 8 Experiments

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  1. Chapter 8Experiments

  2. The Classical Experiment • The most conventional type of experiment involves three major pairs of components: • 1) independent and dependent variables • 2) pre-testing and post-testing • 3) experimental and control groups

  3. Independent and dependent variables • an experiment examines the effect of an independent variable on a dependent variable • the independent variable takes the form of an experimental stimulus, which is either present or absent • the stimulus is a dichotomous variable, having two attributes, present or not present

  4. Independent and dependent variables • the experimenter compares what happens when the stimulus is present to what happens when it is not • the independent and dependent variables appropriate to experimentation are nearly limitless • a given variable might serve as an independent variable in one experiment and as a dependent variable in another

  5. Independent and dependent variables • to be used in a experiment, both independent and dependent variables must be operationally defined • dependent and independent variables must be operationally defined before the experiment begins

  6. Pre-testing and post-testing • in the simplest experimental design, subjects are measured in terms of a dependent variable (pre-testing), exposed to a stimulus representing an independent variable, and then re-measured in terms of the dependent variable (post-testing) • any differences between the first and last measurements on the dependent variable are then attributed to the independent variable

  7. Experimental and control groups • a control group does not receive the experimental stimulus • using a control group allows the researcher to detect any effects of the experiment itself • the need for control groups in experimentation has been nowhere more evident than in medical research • control groups guard against not only the effects of the experiments themselves but also the effects of any events outside the laboratory during the experiments

  8. Double-blind experiment • a double-blind experiment -> neither the subjects nor the experimenters know which is the experimental group and which the control

  9. Selecting Subjects • probability sampling • randomization • matching • a way to achieve comparability between experimental and control group • similar to quota sampling methods

  10. Variations on Experimental Design • one-shot case study – a single group of subjects is measured on a dependent variable following the administration of some experimental stimulus • one-group pre-test-post-test design -> add a pretest for experimental group but lacks a control group • static-group comparison – that some research is based on experimental and control groups but has no pretests

  11. Validity Issues in Experimental Research

  12. Sources of internal invalidity • internal invalidity refers to the possibility that the conclusions drawn from experimental results may not accurately reflect what has gone on in the experiment itself

  13. 1) history->during the course of the experiment, historical events may occur that will confound the experiment results

  14. 2) maturation->people are continually growing and changing, and such changes affect the results of the experiment

  15. 3) testing->often the process of testing and retesting will influence people’s behaviour, thereby confounding the experimental results

  16. 4) instrumentation->the process of measurement in pre-testing and post-testing brings to light some of the issues of conceptualization and operationalization

  17. 5) statistical regression->sometimes it’s appropriate to conduct experiments on subjects who start out with extreme scores on the dependent variable (gets closer to the mean)

  18. 6) selection biases 7) experimental mortality->attrition

  19. 8) cause time-order->stimulus causing the dependent variable can be challenged, ambiguity about the time order of the experimental stimulus and the dependent variable can arise

  20. 9) diffusion or imitation of treatments-.when experimental and control-group subjects can communicate with each other, experimental subjects could pass on some elements of the experimental stimulus to the control group

  21. 10) compensation

  22. 11) compensatory rivalry->in real-live experiments, the subjects deprived of the experimental stimulus may try to compensate for the missing stimulus by working harder

  23. 12) demoralization->feelings of deprivation within the control group may result in their giving up

  24. Sources of external invalidity • relates to the generalizability of experimental findings to the real world

  25. Natural Experiments • experiments occurs outside controlled settings, in the course of normal social events

  26. Advantage • Isolation of the experimental variable and its impact over time

  27. Weakness • Artificiality due to lab set up

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