The Experimental Method: Understanding Causation through Controlled Experiments, Study Guides, Projects, Research of Design

Download The Experimental Method: Understanding Causation through Controlled Experiments and more Study Guides, Projects, Research Design in PDF only on Docsity! The Experimental Method #What is an experiment? How is it different from other methods? < Purpose: to demonstrate causation, that A ---> B – What are the requirements to demonstrate causality? – Correlation – Order. A must precede B. – Control over other variables – Extraneous variables and alternative explanations – Definitions – Examples The Experimental Method < How are experiments different from other types of research? – Manipulated independent variable – Control of organismic variables either by – Random assignment of units of analysis to conditions of the independent variable, or by – Assignment of each unit to all conditions, with controls on order of presentation – Control of other variables by holding them constant – What are extraneous variables? – Can explain the findings of a study without resorting to the hypothesis. – Lead to an alternative explanation of the findings from the one you had . – “In an airtight experiment, there is only one rival hypothesis: chance.” The Experiment Exercise #How do you do a between-subjects experiment? Doob & Gross as example < Devise a “set-up”, including a cover story if needed < Construct independent variable and way to assign subjects to categories < Figure out how to measure the dependent variable #A student example: the waitress and the mints < Set-up < Independent variable and random assignment < Dependent variable #Walk through instructions for experiment exercise #Further examples of past student experiments Internal Validity #What is internal validity and why do we care? < Definition: extent to which one can be confident that the results as reported support the causal hypothesis being tested (Quotes from Campbell & Stanley, 1966) – “Internal validity is the basic minimum without which any experiment is uninterpretable: Did in fact the experimental treatments maqke a difference in the experimental instance?” – More generally, are the variables that appear to be causally related REALLY causally related, or is the apparent relationship spurious? < Why should we care? Discuss. < What’s the difference between internal and external validity? – External validity asks the question of generalizability: to what populations, settings, treatment variables, and measurement variables can this effect be generalized. < Internal and external validity are often at odds. Why? Internal Validity #Campbell and Stanley: types of pre-experiments, experiments, and quasi-experiments – Pre-experiments X O Or O X O – True experiments: random assignment to conditions X O Or O X O — O O – O – Quasi-experiments – same as experiments, except with no random assignment to conditions Internal Validity #Using these terms, what are the problems with pre- experiments? X O Or O X O #What are the problems with quasi-experiments? X O Or O X O — O O – O (Without random assignment to conditions) #Why are experiments OK? The Darley and Batson Experiment #Design < Sample < Is this a between- or a within-subjects experiment? < “Set-up” < Measurement – Independent variables – Dependent variable < Findings – What is an interaction effect? < Threats to internal validity The Goldberg Experiment #Design < Sample < Is this a between- or a within-subjects experiment? < “Set-up” < Measurement – Independent variables – Dependent variable < Findings < Threats to internal validity