Ninth Edition CoverGraziano & Raulin
Research Methods (9th edition)

Chapter 10 Essay Questions
Single-Variable, Independent-Groups Designs

  1. Explain the logic of the following statement: In research, we want to maximize experimental variance, control extraneous variance, and minimize error variance.

  2. Explain the logic of the F-ratio in analysis of variance.

  3. What features make the use of random assignment of participants to groups such a powerful control procedure?

  4. What distinctions separate the nonexperimental research designs discussed in Chapter 10 from the experimental research designs discussed in the same Chapter?

  5. Compare the pretest-posttest, natural control-group design with the randomized, pretest-posttest, control-group design.

  6. What sources of confounding are controlled by the pretest-posttest, natural control-group design that are not controlled by the ex post facto design?

  7. What methods are used to control extraneous variables?

  8. Explain why we cannot confidently draw causal conclusions from the results of non-experimental procedures.

  9. Does a high between-groups variance in an experiment provide sufficient evidence to conclude that the independent variable affected the dependent variable? Explain.

  10. What is the relationship among these concepts: confounding variables, threats to validity, extraneous variance?

  11. Why is randomization the single best way to control extraneous variance?

  12. Suppose you find a significant difference between groups in an experiment. Are we then justified in inferring that the experimental manipulation caused the difference? Explain.

  13. How do (a) random assignment of participants to conditions and (b) the addition of a control group reduce threats to internal validity?

  14. What are the three sources of between-groups variance in an experiment?

  15. What is the relationship between error variance and individual differences among participants?

  16. Why is randomization the single best way to control extraneous variance?

  17. In terms of the F-test, why is it important to minimize the error variance?

  18. Define ex post facto studies and explain why they are weak designs. What conclusions can you draw from this type of study?

  19. Why is it important to be sure that the groups to be compared in an experiment are equivalent at the start of the study?

  20. Almost all threats to validity are controlled if we include only two control procedures. What are they and what threats are controlled by their inclusion?

  21. Why do we urge researchers to randomize wherever possible?