Experimental Design I. Definition of Experimental Design II. Simple Experimental Design III. Complex Experimental Design IV. Quasi-Experimental Design V. Threats to Validity

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

Experimental Design – Simple Designs 1. Post-test Control Group Designs (t-test) E R X -> O1 C R -> O2 2. Pre-Post-test Control Group Designs (t-test) E R O1 X -> O3 C R O2 -> O4

Experimental Design – Simple Designs (cont.) 3. Soloman Four Group Design (t-test) E1 R X1 -> O1 C1 R -> O2 E2 R O1 X1 -> O3 C2 R O2 -> O4 4. Analysis of Variance (ANOVA) E1 R X1 -> O1 E2 R X2 -> O2 E3 R X3 -> O3

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

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 -

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

Experimental Design – Quasi Experiments 1. One Shot Case Study E O1 X ->O2 2. Non-Equivalent Control Group Design E O1 X -> O3 C O2 -> O4 3. Interrupted Time-Series Design E O1 O2 O3 X O4 O5 O6

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