Control Techniques ♣

1. Control Techniques ♣ Chapter 9 Back to Brief Contents • Introduction  • Randomization • Matching • Counterbalancing • Control of Participant Effects • Control of Experimenter Effects • Likelihood of Achieving Control

2. 9.0 Introduction Back to Chapter Contents • Goal of experimentation ― identify the causal effect of the IV • Must have internal validity to do this • Internal validity requires control of confounding variables • Ways of achieving control • Design of the experiment • Statistical adjustments • Incorporate control techniques into the research design

3. 9.1 Randomization -1 Back to Chapter Contents • Randomization is a statistical control technique to equate groups of participants • This is the most important and basic control technique • Random selection—selecting people at random from a defined population • Insures that the sample selected is representative of the population representative: sample P have the same characteristics as the people in the population • Studies seldom if ever do this because of expense, etc

4. 9.1 Randomization -2 Back to Chapter Contents • Random assignment—randomly assigning participants to treatment groups • Provides maximum insurance that groups are equal • Equates groups because every person has an equal chance of being assigned to each group • Accomplishes this by randomly distributing the extraneous variables over the treatment groups Fig 9.1Tab 9.1

5. 9.1 Randomization -3(end) Back to Chapter Contents • Random Assignment Exercise • Randomly assign 40 children to four different drug conditions using the table of random numbers in appendix D Exhibit 8.1 12 • Logon to www.randomizer.org and use the randomizer in this site to randomly assign 40 children to the four drug conditions

6. 9.2 Matching -1 Back to Chapter Contents • Uses of any of a variety of techniques to equate participants in the treatment groups on specific variables • Advantages of matching • Controls for the variables on which participants are matched • Increases the sensitivity of the experiment

7. 9.2 Matching -2(end) Back to Chapter Contents • Matching by Holding Variables Constant  • Matching by Building the Extraneous Variable into the Research Design  • Matching by Yoked Control  • Matching by Equating Participants 

8. 9.2.1 Holding Variables Constant Back to Chapter Contents • Matches on the variable held constant Fig 9.2 • Disadvantages • Restricts the population size • Restricts generalization to the type of participants in the study 9.2

9. 9.2.2 Building EV into Research Design Back to Chapter Contents • Should be used only when you are interested in the effect of the effect of the extraneous variable Fig 9.3 9.2

10. 9.2.3 Matching by Yoked Control Back to Chapter Contents • Controls the temporal relationship between an event and a response • Brady (1958) • Emotional stress → Ulcer • Stress: Press a lever every 20-sec to avoid shock • Control: receive the same temporal sequence of shock 9.2

11. 9.2.4 Matching by Equating Participants Back to Chapter Contents • Precision control—match case by case Fig 9.4 • Disadvantages • Identifying the variables on which to match • Matching increases as the number of variables on which to match increases • Some variables difficult to match • Frequency distribution control—match on the overall distribution of the selected variables Fig 9.5 • Disadvantage • Combination of variables may be mismatched (e.g.) Age-IQ: (E) Old-high IQ, Young-low IQ (C) Old-low IQ, Young-high IQ 9.2

12. 9.3 Counterbalancing Back to Chapter Contents • Used to control sequencing effects • Type of Sequencing effectsFig 9.6 • Order effect Tab 9.2 arising from the order in which the treatment conditions are administered to P • Carry-over effectTab 9.3 occurs when performance in one treatment condition affects performance in another treatment condition • Counterbalancing procedures • Intrasubject Counterbalancing: The ABBA technique  • Intragroup Counterbalancing

13. 9.3 Counterbalancing - intrasubject Back to Chapter Contents • Intrasubject or ABBA technique — counterbalances on a case-by-case basis • Controls only for linear sequencing effects Tab 9.4 • Nonlinear order effects can be controlled if you use the ABBA plus BAAB counterbalancing Tab 9.5 • Can’t control nonlinear carry-over effects 9.3 ◄

14. 9.3 Counterbalancing – Intragroup -1 Back to Chapter Contents • Intragroup Counterbalancing (e.g.) ABC ACB BAC BCA CAB CBA • Incomplete Counterbalancing (Latin square) Participant Sequence 1 A B D C 2 B C A D 3 C D B A 4 D A C B 9.3 ◄

15. 9.3 Counterbalancing - Intragroup -2 Back to Chapter Contents • Intragroup Counterbalancing • Incomplete Counterbalancing (Latin square) A B E C D D C E B A B C A D E E D A C B C D B E A A E B D C D E C A B B A C E D E A D B C C B D A E 9.3 ◄

16. 9.3 Counterbalancing - Intragroup -3(end) Back to Chapter Contents • Intragroup Counterbalancing • Incomplete Counterbalancing (Latin square) 1,2,n,3,(n-1),4,(n-2),5,… 2,3,n+1,4,… (e.g.) A B F C E D ( p. 282, 283 ) B C A D F E C D B E A F D E C F B A E F D A C B F A E B D C 9.3 ◄

17. 9.4 Control of Participant Effects -1 Back to Chapter Contents • Double Blind Placebo Model • Participants, Experimenter • Blind: the treatment condition administered to P • Deception ― giving the P a bogus rationale for the experiment • provide hypothesis : unrelated or orthogonal; false but plausible

18. 9.4 Control of Participant Effects -2(end) Back to Chapter Contents • Perceptual Control, or Control of Participant Interpretation • Retrospective verbal report • postexperimental inquiry • Concurrent verbal report • sacrifice groups: stopped at a different point • concurrent probing: at the end of each trial • think-aloud technique

19. 9.5 Control of Experimenter Effects -1 Back to Chapter Contents • Control of Recording Errors • Aware of the necessity: ensure the accuracy • Kept blind • Mechanical or electronic device • Control of Experimenter Attribute Errors • Interact with treatment effect? Tab 9.6 • Minimize: Control Attributes that correlate with DV

20. 9.5 Control of Experimenter Effects -2(end) Back to Chapter Contents • Control of Experimenter Expectancy Error • The Blind Technique • The Partial Blind Technique • Automation