15. Is drinking coffee good or bad for you? Is decaf better than caffeinated coffee? Mostpreviousstudiesthathavetriedtoanswersuchquestionshavebeenbasedonsurveysaskingpeopletoreporttheircoffeedrinking....



15. Is drinking coffee good or bad for you? Is decaf better than caffeinated coffee? Mostpreviousstudiesthathavetriedtoanswersuchquestionshavebeenbasedonsurveysaskingpeopletoreporttheircoffeedrinking. In2005,Dr.RobertSuperkopresentedtheresultsofwhatis probablythefirsttrulyexperimentalstudyoftheissue. Subjectswere187volunteers. Theyweredividedintothreegroups. For8weekstheydrank: caffeinatedcoffee(black,3to6cupsper day);decaf(black,3to6cups); nocoffeeatall. Thecoffeedrinkerswereprovidedwithcoffeemachinesandpre-measuredservingsofgroundcoffee. Theresultsofthebloodtestsonsubjects inthisfederallyfundedstudyweremixed. Mostwidelyreportedwasthefactthatforsomesubjects,decaffeinatedcoffeelowered“goodcholesterol”(HDL)significantly,by30%. Forsubjectswhowereoverweight,however,theeffectswerejusttheopposite: forthem,decafboostedHDLlevelsbyabout50%.



a.

Doesthefactthatparticipantswerevolunteersraiseproblemsofbias? How,ifatall,doesvolunteerbiasdifferinexperimentalresearchwheresubjectsarerandomlyassignedascomparedtosurveyresearchwherevolunteerswouldnot,bydefinition,bearandomsample?



b.

Whatothervariables,ifany,mightexplaindifferencesintheeffectsofdifferenttypesofcoffee?



c.

Wasthesamplebigenough? Howcanonestudymakedowith187subjectswhenanother—thepoliostudyinthepreviousexample—required400,000?



May 23, 2022
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