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15. Isdrinkingcoffeegoodorbadforyou? Isdecafbetterthancaffeinatedcoffee? Mostpreviousstudiesthathavetriedtoanswersuchquestionshavebeenbasedonsurveysaskingpeopletoreporttheircoffeedrinking. In2005,Dr.RobertSuperkopresentedtheresultsofwhatis probablythefirsttrulyexperimentalstudyoftheissue. Subjectswere187volunteers. Theyweredividedintothreegroups. For8weekstheydrank: caffeinatedcoffee(black,3to6cupsper day);decaf(black,3to6cups); nocoffeeatall. Thecoffeedrinkerswereprovidedwithcoffeemachinesandpre-measuredservingsofgroundcoffee. Theresultsofthebloodtestsonsubjects inthisfederallyfundedstudyweremixed. Mostwidelyreportedwasthefactthatforsomesubjects,decaffeinatedcoffeeloweredgoodcholesterol(HDL)significantly,by30%. Forsubjectswhowereoverweight,however,theeffectswerejusttheopposite: forthem,decafboostedHDLlevelsbyabout50%. Doesthefactthatparticipantswerevolunteersraiseproblemsofbias? How,ifatall,doesvolunteerbiasdifferinexperimentalresearchwheresubjectsarerandomlyassignedascomparedtosurveyresearchwherevolunteerswouldnot,bydefinition,bearandomsample? Whatothervariables,ifany,mightexplaindifferencesintheeffectsofdifferenttypesofcoffee? Wasthesamplebigenough? Howcanonestudymakedowith187subjectswhenanotherthepoliostudyinthepreviousexamplerequired400,000?

15. Isdrinkingcoffeegoodorbadforyou? Isdecafbetterthancaffeinatedcoffee? 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%.

  1. Doesthefactthatparticipantswerevolunteersraiseproblemsofbias? How,ifatall,doesvolunteerbiasdifferinexperimentalresearchwheresubjectsarerandomlyassignedascomparedtosurveyresearchwherevolunteerswouldnot,bydefinition,bearandomsample?
  2. Whatothervariables,ifany,mightexplaindifferencesintheeffectsofdifferenttypesofcoffee?
  3. Wasthesamplebigenough? Howcanonestudymakedowith187subjectswhenanotherthepoliostudyinthepreviousexamplerequired400,000?

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