Download - How to Conduct On-Farm Trials
Howcanyoudeterminewhetheratreatment(thismightbeanadditive,afertilizer,snakeoil,etc.),cultivar,ormanagementpracticeiseffective?
Testitforyourselfinyourorchard• Treatpart(s)ofyourorchardwiththematerial• Leavepart(s)untreated• Measuretreeresponse
– Yield– Leafanalysis– Nutquality– Etc.
• Compare responseoftreatedversusuntreated
Howdowedecideifsomethingisbetter?
• Weneedatleasttwo‘treatments’sowecanmakeacomparison
• Weneedanobjectivewayofevaluatingthetwotreatments• Statisticscanhelpusdetermineifatreatmentactually
affectsplantperformance
Onaveragewho’staller- menorwomen?
Men’sheights Women’sheights
5’6” 6’0” 6’2” 5’11” 5’10” 5’6” 5’7” 5’2” 5’0” 5’6”
66” 72” 74” 71” 70” 66” 67” 62” 60” 66”
Inoursamplesthereisarangeofheightsofbothmenandwomen.Men’sheightsrangefrom66to74”,women60to67”. Somewomenaretallerthansomemen.
Samplestatistics
• Averagesormeans
men women66” 66”72” 67”74” 62”71” 60”70” 66”
averages 70.6” 64.2”
5’10” 5’4”
( ) 2.645
6660626766=
++++
Wecantaketheaverageofeachgroup,butwiththevariabilityinmen’sheightsandinwomen’sheights,howdoweknowifthesenumbersreallydifferent?
• Westartbyevaluatingthespread(statisticiansusemeasuresofvariance orstandarddeviation)
Freq
uency
Value(women’sheight)
5’1”5’2”5’3”5’4”5’5”5’6”5’7”
Mean(average)
StandardDeviation
coefficientofvariation = standarddeviation
mean ×100
standarddeviation = variance�
AnalysisofVariance(ANOVA)usingMicrosoftExcel
InMicrosoftExcel,enterthedataintwocolumns,oneforeach‘treatment’(heremenandwomen)
Select‘Anova:singlefactor’
Select‘Anova:singlefactor’
TellExcelwheretofindyourdataandwhereyouwanttheanalysisoutput
Averages
ThePvaluetellswhetherornotthetwomeansaresignificantlydifferent.ThePvalueistheprobabilitythatthetwomeansarenot different.Inthiscasethereisa0.97%chance
thatthemeansarenotdifferent,ora99.03%chancethattheyreallyaredifferent.
Conclusion:Menaretallerthanwomen!
Note:inscientificresearchwegenerallyconsidermeanstobedifferentiftheANOVAtellsusthereisatleasta90-95%chancethattheyaredifferent.
Orchardresearch• Youneedatleasttwotreatmentssoyoucanmakea
comparison• Treatmentsmustbereplicated (weliketoseeatleast4
replicates)– Thedifferencebetweenreplicatesofeachtreatmentgiveusameasure
ofthevariance(spreadorvariabilityofthedata)– Replicatesshouldbearrangedinarandomizedfashionsothat
differenceinthefield(soilproperties,slope,elevation,water,etc.)donotunfairlyinfluenceonetreatment
Let’ssupposewewanttocomparetwotreatments:AandB.Thesemightbetwofertilizermaterials.Eachpairofpanelsisonereplicate.Werandomlyassigneachpanelinareplicateoneofthetreatments,AorB.
A B A B B A A B B A
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Wecollectdatafromeachpanelindividually,sowehavefive‘A’measurementsandfive‘B’measurements.Measurementscouldbenutyield(shownonfigure),leafnutrientlevels,insectpopulations,etc.
A B A B B A A B B A3375 3455 3020 3220 3140 3005 3065 3220 3010 2925
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Accordingtothetreatmentaveragestreatment‘B’wasbetterthantreatment‘A’
Buttheanalysisofvarianceindicatesthatthereisa25%chancethattheaveragesarenotsignificantlydifferent,sowecannotsaythattreatment‘B’wasreallybetter.Thereisagoodchancethat
differencesbetweentheaverageswerejustcausedbyrandomvariability.
Inthiscase,itlookslikethesnakeoil
decreased nutyield
Otherconsiderations• Sometimesrealrandomizationisnotpossible
– Youcanstillreplicateandconductananalysisofvariance,butthere’sachancethatobserveddifferencewillbefromfieldvariation,notthetreatments
– Replicatesalwaysmustbesampledorharvestedseparately
• Itisagoodideatoleave‘buffer’rowsthatseparatetreatments,soadjacenttreatmentsarenotaffected– Thisisparticularlyimportantwiththingslikespraytreatments,but
evenhedgingonerowwillaffectthenextrow– Treatmentscouldbeappliedtoeveryotherrow
• LocalCooperativeExtensionpersonnelcanhelpyousetupandanalyzefieldresearch