6 - Intro to Design

8/20/2019 6 - Intro to Design

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6Introduction to Design


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• Research design is the glue that holdspieces of the research project together – The sample – The measures – The treatments or programs – The method of assignment

Foundations of Design


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• Causal – Pertaining to a cause-effect question,

hypothesis, or relationship

– omething is causal if it leads to an outcomeor ma!es an outcome happen

– "#ot casual)

Research Design and Causality


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• Temporal precedence• trength of association• Dose-response relationship• Consistently generali a%le else'here• Plausi%ility

• Consideration of competing hypotheses• )uta%le %y e+perimentation• Coherence 'ith e+isting frame'or!s

.ill/s Criteria for Causality


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0nternal alidity


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• The three main types of threats – ingle-group threats – )ulti-group threats – ocial-interaction threats

0nternal alidity


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• 1ccurs in single group post-test orpretest-post-test designs

• Types* – .istory – )aturation – Testing – 0nstrumentation – )ortality "$ttrition2 – Regression to the mean

0nternal alidity – ingle 3roup Threats


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• Deal 'ith single-group threats %y adding asecond group( – Called a control group in an e+periment,

comparison group in quasi-e+periment• 1nce you/&e added a control group, you

need to address the multi-group threats to

internal &alidity

0nternal alidity – ingle 3roup Threats"cont/d42


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• election-history threat• election-maturation threat• election-testing threat• election-instrumentation threat• election-mortality threat

• election-regression threat

0nternal alidity – Types of election 5ias


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• Randomization to treatment groups isthe defining characteristic of anexperiment

0nternal alidity – )ulti-3roup Threats


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Types of Designs


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Random $ssignment &s4 Randomelection


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• Diffusion or imitation of treatment• Compensatory ri&alry• Resentful demorali ation• Compensatory equali ation of treatment

0nternal alidity – ocial-0nteractionThreats


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• Four elements to any research design* – Time – Treatments or programs "0 6predictors2 – )easures or o%ser&ations "D 6outcomes2 – 3roups or indi&iduals

De&eloping a Research Design


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Design #otation


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#otational 7+amples


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Different designs ha&e different'ea!nesses

• Post-test only, t'o-group,randomi ed e+periment

• 'itched-replication,t'o group e+periment


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)ore designs

• Pre-and-post-test, t'o-group,non-equi&alent groups quasi-e+periment

• Time-series e+periment


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• 8hy is internal &alidity so important inresearch design9

• 8hat is the purpose of randomi ation inresearch design9

Discuss and De%ate

6 - Intro to Design

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