CHAPTER 1
Sources of Variation Section 1.1
1.1.10 Color of asignistheexplanatoryvariablewithwhite,yellow, andredbeingthelevels.
1.1.1 B.
1.1.11
1.1.2 B & C. 1.1.3 A.
Observed Variation in:
1.1.4 C.
f.whetherthestudent obeyedthesign
1.1.5 E. 1.1.6 B.
60.34if rigid librarian number of uses for items= 1.1.7 predicted { 92.19if eccentric poet 1.1.8 a. The inclusion criteria are having a clinical diagnosis of mild to moderate depression without any treatment four weeks prior and duringthestudy. b. The purpose of randomly assigning subjects to the groups is to makegroupsverysimilarexceptfortheonevariable(swimmingwith dolphinsornot)thattheresearchersimpose.Volunteeringforagroup couldintroduceaconfoundingvariable. c. Itwasimportantthatthesubjectsinthecontrolgroupswimevery day withoutdolphinssothatthiscontrolgroupdoeseverything(including swimming) that the experimental group does except that whentheyswimtheydon’tdoitinthepresenceof dolphins.Without thiswewouldn’tknowwhetherjustswimmingcausesthedifference inthereductionof depressionsymptoms. d. Yes,thisisanexperimentbecausethesubjectswererandomlyassignedtothetwogroups. 1.1.9.
Observed variation in: d.substantialreduction indepressionsymptoms
Sources of explained variation
Inclusion criteria a.swimmingwith dolphinsornot • b.mildtomoderate depression • c.nouseof antidepressantdrugs orpsychotherapyfour weekspriortothe study Design • e.swimming • f.stayingonanisland fortwoweeksduring thestudy
Sources of unexplained variation • g.problemsinthe personallivesof thesubjectsduring thestudy • h.illnessof subjectsduring thestudy
Inclusion criteria • c.timeof day • e.ageof subject
Sources of explained variation
Sources of unexplained variation
a.colorof the sign
b.whetherthesubject wasleft-handedor right-handed d.attitudeof student e.ageof subject
1.1.12 a. Thevalue6.21representstheoverallmeanquizscore,5.50represents the group mean quiz score for people who used computer notes, and 6.92representsthegroupmeanscoreforpeoplewhousedpapernotes. b. Welooktoseehowfar6.92and5.50arefromoneanotherorfrom theoverallmeanof 6.21todeterminewhetherthenote-takingmethod mightaffectthescore. c. The number 1.76 represents the typical deviation of an observationfromtheexpectedvalue,inthiscase,fromtheoverallmean.The number1.61representsthetypicaldeviationof anobservationafter creatingamodelthattakesintoaccountwhetherthepersonisusing computerorpapernotes. d. Becausethestandarddeviationof theresidualsrepresentstheleftovervariation,wecanseethatafterincludingthetypeof notesasan explanatoryvariableinourmodeltheunexplainedvariationhasbeen reduced(downto1.61from1.76).Thistellsusthatknowingthetype of note-takingmethodenablesustobetterpredictscores. 1.1.13 Random assignment should make the two groups very similar with regard to variables like intelligence, previous knowledge, or any other variable and thus likely eliminate possible confoundingvariables. 1.1.14 a. This table shows us possible confounding variables but then shows that subjects in the two groups are quite similar with regard to these characteristics, thus ruling out these possible confoundingvariables. b. We would want the p-values to be large, so we could say that we havelittletonoevidencethatthereisadifferenceinmeanage, proportionof males,etc.betweenthetwogroups.Wewantourgroups tobeverysimilargoingintothestudy,soacausalconclusionispossibleif wefindasmallp-valueafterapplyingthetreatment(s).
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