Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Experimental designs

3,486 views

Published on

let share

  • Be the first to comment

Experimental designs

  1. 1. ExperimentalResearch Designs
  2. 2. Experimental Design Advantages  Best establishes cause-and-effect relationships Disadvantages  Artificiality of experiments  Feasibility  Unethical
  3. 3. Causality Temporal precedence Covariation between IV and DV Eliminate alternative explanations
  4. 4. Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental
  5. 5. Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental
  6. 6. Simple True Experimental Characteristics Types Variations
  7. 7. Characteristics of True Designs Manipulation (treatment) Randomization Control groupCharacteristics of simple true designs One IV with 2 levels (T, C) One DV
  8. 8. Types Randomized posttest control group design Randomized pretest-posttest control group design
  9. 9. Randomized posttest control group design R T Post R C Post
  10. 10. Randomized pretest-posttest control groupdesign R Pre T Post R Pre C Post
  11. 11. Advantages & Disadvantages Advantages of pretest design  Equivalency of groups  Can measure extent of change  Determine inclusion  Assess reasons for and effects of mortality Disadvantages of pretest design  Time-consuming  Sensitization to pre-test
  12. 12. Solomon four-group design R Pre T Post R Pre C Post R T Post R C Post
  13. 13. Variations Independent groups (between groups) Repeated measures (within groups)
  14. 14. Repeated Measures Design Advantages:  Fewer subjects needed (less costly)  Sensitive to finding statistical differences Disadvantages:  Order effect (practice, fatigue, carry-over)
  15. 15. Dealing with Order Effects Counterbalancing  n!  Latin squares
  16. 16. Latin Squares 1 2 3 4 A B D CRow 1 (60) (0) (120) (180) B C A DRow 2 (0) (180) (60) (120) C D B ARow 3 (180) (120) (0) (60) D A C BRow 4 (120) (60) (180) (0)
  17. 17. Dealing with Order Effects Counterbalancing  n!  Latin squares  Randomized blocks Time interval between treatments
  18. 18. Variations Independent groups (between) vs. repeated measures (within) designs Consider external validity when deciding which design to use.
  19. 19. Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental Pre-Experimental
  20. 20. Characteristics of True Designs Manipulation (treatment) Randomization Control groupCharacteristics of simple true designs One IV with 2 levels (T, C) One DV
  21. 21. Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs
  22. 22. Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs
  23. 23. Randomized matched control groupdesign M R T Post M R C Post • Used in small samples ∀ ↑ cost in time & money
  24. 24. Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs
  25. 25. Increased Levels of IV Provides more complete information about the relationship between the IV & DV Detects curvilinear relationships Examines effects of multiple treatments
  26. 26. Reward Amount $0 $1 $2 $3DV Performance level (% complete) Amount of reward promised ($) IV
  27. 27. Increased Levels of IVDV Performance level (% complete) Amount of reward promised ($) IV
  28. 28. Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs
  29. 29. Factorial Design >1 IV (factor) Simultaneously determine effects of 2 or more factors on the DV (real world) Between Factor vs. Within Factor ID’d by # of factors and levels of factors 2X2
  30. 30. Do differing exercise regimens (hi,med, lo intensity) have the same effecton men as they do on women? 3 X 2 (Exercise Regimen X Gender) 2 factors  Exercise Regimen – 3 levels  Gender – 2 levels  Between factors  DV?  Experimental IVs or Participant IVs?
  31. 31. Gender Male Female HighExerciseIntensity Medium Low
  32. 32. Do strength gains occur at the same rate in menas they do in women over a 6 mo. training period?Measurements are taken at 0, 2, 4, 6 mo. 2 X 4 (Gender X Time) ? factors  Time – 4 levels  Gender – 2 levels  Between or within factors?  DV?  Experimental IVs or Participant IVs?
  33. 33. Time 0 mo. 2 mo. 4 mo. 6 mo.Gender Male Female
  34. 34. Cell means, Margin meansMain Effects, Interactions Time 0 mo. 2 mo. 4 mo. 6 mo. Gender Male 50 70 90 130 85 Female 30 60 75 90 64 40 65 83 110 74 Cell means Margin means Grand mean
  35. 35. Time 0 mo. 2 mo. 4 mo. 6 mo.Gender Male 50 70 90 130 85 Female 30 60 75 90 64 40 65 83 110 74
  36. 36. Parallel lines indicate no Is there a main interaction. effect? Interaction of Exercise Intensity and Gender 70 65VO2 Max (ml/kg/min) 60 55 Male 50 Female 45 40 35 High Medium Low Exercise Intensity
  37. 37. Is there a main Interaction of Exercise Intensity and Gender effect? 70 65VO2 Max (ml/kg/min) 60 55 High Medium 50 Low 45 40 35 Male Female Gender
  38. 38. Non-parallel lines indicate an there Is interaction. a main Interaction of Gender and Time effect? 140 120Weight Lifted (lbs.) 100 80 Male 60 Female 40 20 0 0 mo. 2 mo. 4 mo. 6 mo. Time
  39. 39. Is there a main Interaction Between Gender and Time effect? 140 120Weight Lifted (lbs.) 100 0 mo. 80 2 mo. 60 4 mo. 6 mo. 40 20 0 Male Female Gender
  40. 40. Interpretation Always interpret the interaction first (graphical) If no significant interaction, interpret main effects
  41. 41.  Advantages of factorial designs:  Greater protection against Type I error  More efficient  Can examine the interaction Disadvantages: ↑ subject # for between factor designs Consider external validity when deciding which design to use.
  42. 42. IV A: Exposure to Violence – violent vs.nonviolent videoIV B: Gender – male vs. female B1DV: # ads recalled (0-8) B2 9 B 1 2 1 1 5 3A 5 2 9 5 7 5 5 1 1 2 A
  43. 43. IV A: Exposure to Violence – violent vs.nonviolent videoIV B: Gender – male vs. female B1DV: # ads recalled (0-8) B2 9 A: Yes B: No 5 AxB: Yes 1 1 2 A
  44. 44. Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs
  45. 45. Do strength gains occur at the same rate in menas they do in women over a 6 mo. training period?Measurements are taken at 0, 2, 4, 6 mo. Time 0 mo. 2 mo. 4 mo. 6 mo. Gender Male 50 70 90 130 85 Female 30 60 75 90 64 40 65 83 110 74
  46. 46. Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental
  47. 47. Characteristics of True Designs Manipulation (treatment) Randomization Control group Less control More real-world Program evaluation
  48. 48. Randomized posttest control group design R T Post R C Post
  49. 49. Randomized pretest-posttest control groupdesign R Pre T Post R Pre C Post
  50. 50. Quasi-experimental Designs One group posttest-only design One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  51. 51. Quasi-experimental Designs One group posttest-only design One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  52. 52. Randomized posttest control group design R T Post R C Post
  53. 53. One group posttest-only design(One shot study) T Post No control of IV threats Use?
  54. 54. Quasi-experimental Designs One shot study One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  55. 55. Randomized pretest-posttest control groupdesign R Pre T Post R Pre C Post
  56. 56. One group pretest-posttest design Pre T Post •History •Maturation •Testing Use control group •Instrument decay •Regression
  57. 57. Quasi-experimental Designs One shot study One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  58. 58. Randomized posttest control group design R T Post R C Post
  59. 59. Non-equivalent control group design(Static group comparison design) T Post C Post •Selection bias
  60. 60. Quasi-experimental Designs One shot study One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  61. 61. Randomized pretest-posttest control groupdesign R Pre T Post R Pre C Post
  62. 62. Non-equivalent control grouppretest-posttest design Pre T Post Pre C Post •Can check selection bias
  63. 63. Quasi-experimental Designs One shot study One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  64. 64. Time series Pre Pre Pre Pre T Post Post Post Post
  65. 65. Quasi-experimental Designs One shot study One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  66. 66. Quasi-experimental Designs One shot study One group pretest-posttest design Non-equivalent control group design Non-equivalent control group pretest-posttest design Time series Single subject designs (Case study) Developmental designs
  67. 67. Developmental Research Designs Longitudinal Cross Sectional Powerful (within  Less time consuming subject)  Cohorts problem Time consuming Attrition Testing effect
  68. 68. Choosing a Research Design Best addresses the problem Ethics Cost in time and money Validity (internal & external)

×