Unformatted text preview:

DesignInternal ValiditySlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Introduction to designTypes of designsSlide 36KNR 295Research DesignSlide 1DesignCh. 6 – Internal ValidityKNR 295Research DesignSlide 2Internal ValidityCause and effectCause…“Function: transitive verbInflected Form(s): caused; caus·ingDate: 14th century1 : to serve as a cause or occasion of : MAKE2 : to effect by command, authority, or force- caus·er noun”*from Merriam-Webster onlineKNR 295Research DesignSlide 3Internal ValidityCause and effectEffect…“Function: nounEtymology: Middle English, from Middle French & Latin; Middle French, from Latin effectus, from efficere to bring about, from ex- + facere to make, do -- more at DODate: 14th century1 something that inevitably follows an antecedent (as a cause or agent) ”*from Merriam-Webster onlineKNR 295Research DesignSlide 4Internal ValidityCause and effectInternal validity is a “zero-generalizability concern”KNR 295Research DesignSlide 5Internal ValidityCause and effectSo…did the treatment you used cause the measurement you took to be what it was?Or…to what extent did the treatment you used influence the measurement you took?KNR 295Research DesignSlide 6Internal ValidityEstablishing cause and effectExample: Does beer make you happy?Temporal precedencebeerhappinessKNR 295Research DesignSlide 7Internal ValidityEstablishing cause and effectExample: Does beer make you happy?Covariation of cause and effectIf beer then happyIf not beer then not happyIf more beer then more happyIf less beer then less happyKNR 295Research DesignSlide 8Internal ValidityEstablishing cause and effectExample: Does beer make you happy?No plausible alternative explanations“Never drink alone”…social causes?To drink, you need to be flush…it’s an economic difference?Drinkers experience smoke too…it’s all down to ciggies?When you drink you go to the loo more often…something to do with bladder swelling/emptying?Rank – most plausible? - least plausible?KNR 295Research DesignSlide 9Internal ValiditySingle group threatsSticking with the beer idea…Imagine you take a group of students, and give them a dose of beer. You might measure their happiness just once at the end, or you might measure them both before and after the beer dose…KNR 295Research DesignSlide 10Internal ValiditySingle group threatsSticking with the beer idea…Give beerMeasure happinessMeasure happinessMeasure happinessGive beerKNR 295Research DesignSlide 11Internal ValiditySingle group threatsSticking with the beer idea…History ThreatIt’s not the beer. It’s some other major historical event that influenced your group’s happiness…Perhaps on the day of the test, Saddam decided to pack it in, and everyone simultaneously found out that the recession was a big mass-induced dream state, awaking to find that the world was infinitely happier than they had first thought?Plausible?KNR 295Research DesignSlide 12Internal ValiditySingle group threatsSticking with the beer idea…Maturation ThreatAs people get older, they get happier. You took your first measurement during your group’s teenage angst years, then waited until the wisdom, wonder and general delight of 40ish life settled in before taking the second measurement[can be anything related to general “internal” change in people – any “big event” external to the person causing the change is generally regarded as a history threat]Plausible?KNR 295Research DesignSlide 13Internal ValiditySingle group threatsSticking with the beer idea…Testing Threat(Pre-post only)Measuring happiness made participants focus on their degree of happiness – if they were unhappy, they resolved to buckle up, and cheer up. If they were happy they were made aware of this and were therefore delighted to be so well-adjusted Plausible?KNR 295Research DesignSlide 14Internal ValiditySingle group threatsSticking with the beer idea…Instrumentation Threat (pre-post again)A couple of possibilities…The group are scored with different instruments on each occasion. The second is more sensitive than the first. The group’s happiness doesn’t change, but the scores arising from the instruments differ anywayThe person giving out the happiness instrument is such a happy-go-lucky lass that she infects everyone else with her sense of “joi de vivre” (experimenter as instrument)- the longer she’s around the happier you feelPlausible?KNR 295Research DesignSlide 15Internal ValiditySingle group threatsSticking with the beer idea…Mortality ThreatAs the study wears on and the beer starts to have its inevitable effect, many people are past the stage of being happy and are approaching that other unfortunate stage of influence…but they aren’t around for the happiness measurement at the end of the studyPlausible?KNR 295Research DesignSlide 16Internal ValiditySingle group threatsSticking with the beer idea…Regression Threat[The Fugawe Tribe]When you look at the scores of your group on the pre-test, you notice that they are unusually low…This situation, where for any reason scores are just by chance suppressed on the first measurement, will probably result in artificially higher scores (in comparison to the first) on the second readingIt’s not that the treatment is having an effect, it’s that the scores are just going back to normalNormally occurs when selecting a group by pre-test scores…Plausible?KNR 295Research DesignSlide 17Internal ValiditySingle group threatsSticking with the beer idea…Regression ThreatYou want to find out if the effect even works on really unhappy people. So you get 200 grad students to fill out a happiness questionnaire, and select only the lowest 25% for your study.Lo and behold, after a good dose of beer, they all score higher on the hap-o-meter!Why?Plausible?KNR 295Research DesignSlide 18Internal ValiditySolving single group threatsAdd a control groupThe only difference between the control group and the treatment group should be the presence or absence of the treatmentSometimes this means you need multiple control groupsOften, it still


View Full Document

ISU KNR 295 - Design

Download Design
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Design and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Design 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?