Experimentation

What experiments are not: Two commonsense uses of “experiment”: – any study – to “try something out” – …both of these understandings are flawed.

What Experiment are: Experiments test causal relationships. A causal relationship has three elements: – Stable temporal ordering – An association between the phenomena studied – No alternative explanations for that association. Among all the methods available to social researchers, only experiments can verify all three of these elements that define a causal relationship.

“Real” experiments have three necessary conditions: A hypothesis; The modification of something in a specific situation; The comparison of outcomes with and without the modification.

Experimentation requires that “subjects” (“Ss”) be randomly assigned to “treatment” and “control” groups. The meaning of “random assignment” The purpose of random assignment – Attainment of comparable groups – Even distribution of bias Methods of random assignment – Random process, like coin flips – Random number generator – Computer-based assignment

Experiment designs vary, but must have 7 essential features to be true experiments: Random assignment A “treatment” or “independent” variable A “dependent” variable Pretesting Post-testing An “experimental” or “treatment” group A “control” group

Some examples of experimental and pseudo-experimental design “Pre-experimental designs” (shortcuts) – Case study (no comparison, no pretest) – Static group comparison (no random assignment, no pretest) Classical Experimental Design – With dichotomous independent variable – With continuous independent variable – With more than one independent variable Quasi-experimental Designs – Two-group, post-test only with random assignment – Time series designs with one group or one subject – Latin square – Solomon n-group – Field experiments

Issues regarding internal and external validity Internal Validity – Selection Bias – History Effects – Maturation – Testing Effects – Instrument Reliability – Contamination – Experimenter Expectancy External Validity – Realism (is setting or task “real”?) experimental realism mundane realism – Reactivity (are Ss only reacting to experiment?) The Hawthorne effect response to demand characteristics the placebo effect