Experimental Design

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Experimental Design
I. Definition of Experimental Design
II. Simple Experimental Design
III. Complex Experimental Design
IV. Quasi-Experimental Design
V. Threats to Validity
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Experimental Design - Definition
Control over the sequence and proportion of the
independent variable involving 1) at least two
conditions (i.e. an independent variable) 2)
random assignment of subjects to conditions and
3) the measurement of some outcome (i.e.
dependent variable
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Experimental Design Simple Designs
1. Post-test Control Group Designs (t-test)
E R X -gt O1 C R -gt
O2
2. Pre-Post-test Control Group Designs (t-test)
E R O1 X -gt O3 C R
O2 -gt O4
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Experimental Design Simple Designs (cont.)
3. Soloman Four Group Design (t-test) E1 R
X1 -gt O1 C1 R
-gt O2 E2 R O1 X1 -gt O3
C2 R O2 -gt O4
4. Analysis of Variance (ANOVA)
E1 R X1 -gt O1 E2 R X2 -gt
O2 E3 R X3 -gt O3
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Experimental Design Complex Designs
1. Completely Randomized Designs (CRD)

(This example is a 2x3 CRD)
  C-E1 C-E2 C-E3
R-E1 O11 O12 O13 R-E2 O21 O22
O23
Main Effects Interaction Effects
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Experimental Design Complex Designs (cont.)

• Incomplete Designs (IRD)
• Split Plot Design (This example is a 2x3
  SPD)
• C-E1 C-E2 C-E3
• R-E1 - O12 O13
• R-E2 O21 O22 -

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Experimental Design Complex Designs (cont.)

• 3. Repeated Measures Designs (RMD)
• Latin Square Design ( This example is
  a 4x4 LSD)
• O1 O2 O3 O4
  O2 O3 O4 O1
  
  O3 O4 O1 O2
  O4 O1 O2 O3

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Experimental Design Quasi Experiments
1. One Shot Case Study E O1 X -gtO2
2. Non-Equivalent Control Group Design
E O1 X -gt O3 C O2 -gt O4
3. Interrupted Time-Series Design E O1 O2 O3
X O4 O5 O6
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Experimental Design - Threats to Validity
1. History confounding of IV over time
2. Maturation age / experience contaminate
3. Testing subjects come to understanding IV
4. Regression to the Mean extreme scores regress
5. Selection of Participants non-random
assignment
6. Mortality subject attrition
7. Diffusion of Treatments lack of control group