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Experiment Basics: Designs

Experiment Basics: Designs. Psych 231: Research Methods in Psychology. participants. Colored words. Colored words. BW words. Test. Test. participants. Test. BW words. Within-subjects designs All participants participate in all of the conditions of the experiment.

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Experiment Basics: Designs

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  1. Experiment Basics: Designs Psych 231: Research Methods in Psychology

  2. participants Colored words Colored words BW words Test Test participants Test BW words • Within-subjects designs • All participants participate in all of the conditions of the experiment. • Between-subjects designs • Each participant participates in one and only one condition of the experiment. Between vs. Within Subjects Designs

  3. Clock Chair Cab Clock Chair Cab Colored words participants Test BW words • Advantages • Independence of groups (levels of the IV) • Disadvantages • Individual differences between the people in the groups • Excessive variability • Non-Equivalentgroups Between subjects designs

  4. participants Colored words Colored words BW words Test Test participants Test BW words • Between-subjects designs • Each participant participates in one and only one condition of the experiment. • Within-subjects designs • All participants participate in all of the conditions of the experiment. Between vs. Within Subjects Designs

  5. Advantages: • Don’t have to worry about individual differences • Fewer participants are required • Disadvantages • Range effects • Order effects: • Carry-over effects • Progressive error Within subjects designs

  6. Range effects – (context effects) can cause a problem • The range of values for your levels may impact performance (typically best performance in middle of range). • Since all the participants get the full range of possible values, they may “adapt” their performance (the DV) to this range. Within subjects designs

  7. Condition 1 Condition 2 test test • Carry-over effects • Transfer between conditions is possible • Effects may persist from one condition into another • e.g. Alcohol vs no alcohol experiment on the effects on hand-eye coordination. Hard to know how long the effects of alcohol may persist. How long do we wait for the effects to wear off? Order effects

  8. Progressive error • Practice effects – improvement due to repeated practice • Fatigue effects – performance deteriorates as participants get bored, tired, distracted Order effects

  9. Counterbalancing is probably necessary • This is used to control for “order effects” • Ideally, use every possible order • (n!, e.g., AB = 2! = 2 orders; ABC = 3! = 6 orders, ABCD = 4! = 24 orders, etc). • All counterbalancing assumes Symmetrical Transfer • The assumption that AB and BA have reverse effects and thus cancel out in a counterbalanced design Dealing with order effects

  10. Colored words BW words Test Test participants BW words Colored words Test Test • Simple case • Two conditions A & B • Two counterbalanced orders: • AB • BA Note: this becomes a factorial design Counterbalancing

  11. Often it is not practical to use every possible ordering • Partial counterbalancing • Latin square designs – a form of partial counterbalancing, so that each group of trials occur in each position an equal number of times Counterbalancing

  12. A B C D Order 1 B C D A Order 2 C D A B Order 3 D A B C Order 4 • Example: consider four conditions • Recall: ABCD = 4! = 24 possible orders 1) Unbalanced Latin square: each condition appears in each position (4 orders) Partial counterbalancing

  13. 2) Balanced Latin square: each condition appears before and after all others (8 orders) • Example: consider four conditions • Recall: ABCD = 4! = 24 possible orders Partial counterbalancing

  14. Mixed designs • Treat some factors as within-subjects (participants get all levels of that factor) and others as between-subjects (each level of this factor gets a different group of participants). • This only works with factorial (multi-factor) designs Mixed factorial designs

  15. You need to describe: • How many factors • How many levels of each factor • Whether the factors are within or between groups • e.g., 2 (shallow/deep processing) x 2 (abstract/concrete) mixed groups factorial design Describing your design

  16. You need to report: • The main effects • Depth of processing • Word Type • The interaction • For each report the means (in the case of the main effects, report the marginal means) and the statistical outcomes (the ANOVA results) • Depth of processing: F(1,226) = 98.6, p < 0.001 • Word type: F(1,226) = 34.0, p < 0.001 • Interaction: F(1,226) = 5.0, p < 0.026 • Do this with within complete sentences and paragraphs • Feel free to supplement the text with a graph if it helps with clarity. Describing your results

  17. Relevant stuff from Ex1 • Variables • types, operationalizing • IV: methods of manipulation, getting the right range • DV: measurement • Validity and Reliability • Sampling • Control • Experimental Designs • Vocabulary • Single factor designs • Between & Within • Factorial designs Exam 2 Topics (Chpts 4, 6, 11)

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