Experimental Designs

Experimental Designs

Classifying Experimental Designs • Observations in a study can be divided into two components: • Signal: The key variable—the construct you’re trying to measure • Noise: All random factors in the situation that make it harder to see the signal

Observation Signal Noise Classifying Experimental Designs

Signal Noise Classifying Experimental Designs • You want the signal to be high relative to the noise

Classifying Experimental Designs • Classify experimental designs into to categories • Signal Enhancers • Factorial designs • Noise Reducers • Correlated groups designs • Matched pairs, repeated measures, naturally-occurring pairs

Single IV Designs • The basic two-group design Independent Variable: Customer Hearing Experimental group Control group Customers were deaf Customers were hearing

Single IV Designs • Independent groups • Randomly assigned to groups • Correlated groups • Matched pairs • Repeated measures • Natural pairs

Single IV Designs • Advantages of independent-groups designs • Simplicity • In some contexts, it is impossible to use correlated groups • Advantages of correlated-groups designs • Control—we have greater certainty of equality • Statistical benefits

Signal between-groups variability statistic = error variability Noise Statistical benefits • Two sources of variability in your data: • The IV, or between-groups variability • Error variability, or within-groups variability

Single IV Designs • The multiple-group design Independent Variable: Type of Noise Experimental group 2 Experimental group 3 Experimental group 1 White noise Music No noise

between-groups variability statistic = within-groups variability Single IV Designs • The multiple-group design • Analysis: Oneway ANOVA

Post-hoc comparisons Single IV Designs • The multiple-group design: Analysis Independent Variable: Type of Noise Experimental group 2 Experimental group 3 Experimental group 1 White noise Music No noise

Single IV Designs • The multiple-group design: Analysis Independent Variable: Type of Noise Experimental group 2 Experimental group 3 Experimental group 1 White noise Music No noise Post-hoc comparisons

Factorial Designs • Multiple IV designs • Signal enhancers

Factor A (First IV) Level A2 Level A1 A1B1 A2B1 Level B1 Factor B (Second IV) A1B2 A2B2 Level B2 Levels: Subdivisions of factors Factors: Major independent variables

Main effect of time; no effectof setting Time 4 hr/wk 1 hr/wk 5 7 6 Inside Setting 5 7 6 Outside 5 7 Analysis, example 1

Main effect of time Analysis, example 1

Main effect of setting Analysis, example 1

Main effect of setting,no effectof time Time 4 hr/wk 1 hr/wk 5 5 5 Inside Setting 7 7 7 Outside 6 6 Analysis, example 2

Main effect of bothtime and setting Time 4 hr/wk 1 hr/wk 5 7 6 Inside Setting 7 9 8 Outside 6 8 Analysis, example 3

Main effect of bothtime and setting, and aninteraction Time 4 hr/wk 1 hr/wk 5 5 5 Inside Setting 5 7 6 Outside 5 6 Analysis, example 4

Basicinteraction Analysis, example 4

Main effect of bothtime and setting, and aninteraction Time 4 hr/wk 1 hr/wk 7 5 6 Inside Setting 5 7 6 Outside 6 6 Analysis, example 5

Crossover interaction Analysis, example 5

Experimental Designs