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Experimental Research Designs. Experimental Design Advantages  Best establishes cause-and-effect relationships Disadvantages  Artificiality of experiments.

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Presentation on theme: "Experimental Research Designs. Experimental Design Advantages  Best establishes cause-and-effect relationships Disadvantages  Artificiality of experiments."— Presentation transcript:

1 Experimental Research Designs

2 Experimental Design Advantages  Best establishes cause-and-effect relationships Disadvantages  Artificiality of experiments  Feasibility  Unethical

3 Causality Temporal precedence Covariation between IV and DV Eliminate alternative explanations

4 Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental

5 Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental

6 Simple True Experimental Characteristics Types Variations

7 Characteristics of True Designs Manipulation (treatment) Randomization Control group Characteristics of simple true designs One IV with 2 levels (T, C) One DV

8 Types Randomized posttest control group design Randomized pretest-posttest control group design

9 Randomized posttest control group design RTPost RCPost

10 Randomized pretest-posttest control group design RPreTPost RPreCPost

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 Solomon four-group design RPreTPost RPreCPost RTPost RCPost

13 Variations Independent groups (between groups) Repeated measures (within groups)

14 Repeated Measures Design Advantages:  Fewer subjects needed (less costly)  Sensitive to finding statistical differences Disadvantages:  Order effect (practice, fatigue, carry-over)

15 Dealing with Order Effects Counterbalancing  n!  Latin squares

16 Latin Squares 1234 Row 1 A (60) B (0) D (120) C (180) Row 2 B (0) C (180) A (60) D (120) Row 3 C (180) D (120) B (0) A (60) Row 4 D (120) A (60) C (180) B (0)

17 Dealing with Order Effects Counterbalancing  n!  Latin squares  Randomized blocks Time interval between treatments

18 Variations Independent groups (between) vs. repeated measures (within) designs Consider external validity when deciding which design to use.

19 Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental Pre-Experimental

20 Characteristics of True Designs Manipulation (treatment) Randomization Control group Characteristics of simple true designs One IV with 2 levels (T, C) One DV

21 Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs

22 Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs

23 Randomized matched control group design MRTPost MRCPost Used in small samples  cost in time & money

24 Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs

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 Performance level (% complete) Amount of reward promised ($) DV IV

27 Increased Levels of IV Performance level (% complete) Amount of reward promised ($) DV IV

28 Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs

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 Do differing exercise regimens (hi, med, lo intensity) have the same effect on 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

32 Do strength gains occur at the same rate in men as 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

34 Cell means, Margin means Main Effects, Interactions Cell means Margin means Grand mean

35 Interaction& Main Effects Interaction - combined effect of the factors on the dependent variable Main effect – the deviation of two or more treatment means from the grand mean

36

37 Parallel lines indicate no interaction. Is there a main effect?

38 Is there a main effect?

39 Non-parallel lines indicate an interaction. Is there a main effect?

40 Is there a main effect?

41 Interpretation Always interpret the interaction first (graphical) If no significant interaction, interpret main effects

42 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.

43 IV A: Exposure to Violence – violent vs. nonviolent video IV B: Gender – male vs. female DV: # ads recalled (0-8) 12 1153 2957 55 A B 1 5 9 12 A B1B1 B2B2

44 1 5 9 12 A B1B1 B2B2 A: Yes B: No AxB: Yes

45 Complex True Experimental Randomized matched control group design Increased levels of IV Factorial design Multiple DVs

46 Do strength gains occur at the same rate in men as they do in women over a 6 mo. training period? Measurements are taken at 0, 2, 4, 6 mo.

47 Types of Experimental Designs Simple True Experimental Complex True Experimental Quasi-Experimental

48 Characteristics of True Designs Manipulation (treatment) Randomization Control group Less control More real-world Program evaluation

49 Randomized posttest control group design RTPost RCPost

50 Randomized pretest-posttest control group design RPreTPost RPreCPost

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 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

53 Randomized posttest control group design RTPost RCPost

54 One group posttest-only design (One shot study) TPost No control of IV threats Use?

55 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

56 Randomized pretest-posttest control group design RPreTPost RPreCPost

57 One group pretest-posttest design PreTPost History Maturation Testing Instrument decay Regression Use control group

58 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

59 Randomized posttest control group design RTPost RCPost

60 Non-equivalent control group design (Static group comparison design) TPost CPost Selection bias

61 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

62 Randomized pretest-posttest control group design RPreTPost RPreCPost

63 Non-equivalent control group pretest-posttest design PreTPost PreCPost Can check selection bias

64 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

65 Time series Pre Pre Pre Pre T Post Post Post Post

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 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

68 Developmental Research Designs Longitudinal Powerful (within subject) Time consuming Attrition Testing effect Cross Sectional Less time consuming Cohorts problem

69 Choosing a Research Design Best addresses the problem Ethics Cost in time and money Validity (internal & external)

70 Experimental design 5 m Subambient CO2 tunnelElevated CO2 tunnel 250 ppm 500 ppm 370 ppm

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