ChoosingAppropriateGraphs or

Whattodowithallthatdata…

BarGraphsareappropriatefordatathatarenon‐numericalanddiscreteforatleastonevariable,i.e.theyaregroupedintoseparatecategories.Therearenodependentorindependentvariables.Importantfeaturesofthistypeofgraphinclude:

• Dataarecollectedfordiscontinuous,non‐numericalcategories(e.g.place,colour,andspecies)sothebarsdonottouch.

• Datavaluesmaybeenteredonorabovethebarsifyouwish.• Multiplesetsofdatacanbedisplayedside‐by‐sidefordirectcomparison(e.g.males

andfemalesofthesameagegroup).• Axesmaybereversedsothatthecategoriesareonthex‐axis,i.e.thebarscanbe

verticalorhorizontal.Whentheyarevertical,thesegraphsaresometimescalledcolumngraphs(MSExcelusesthisnameforverticalbargraphs).

Histogramsareplotsofcontinuousdataandareoftenusedtorepresentfrequencydistributions,wherethey‐axisshowsthenumberoftimesaparticularmeasurementorvaluewasobtained.Forthisreason,theyareoftencalledfrequencyhistograms.Importantfeaturesofthistypeofgraphinclude:

• Thedataarenumericaland

continuous(e.g.heightorweight)sothebarstouch.(AcolumngraphfromExcelcanbemadeintoahistogram).

• Thex‐axisusuallyrecordstheclassinterval.They‐axisusuallyrecordsthenumberofindividualsineachclassinterval(frequency).

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PieGraphscanbeusedinsteadofbargraphs,generallyincaseswheretherearesixoffewercategoriesinvolved.Apiegraphprovidesstrongvisualimpactoftherelativeproportionsineachcategory,particularlywhereoneofthecategoriesisverydominant.Featuresofpiegraphsinclude:

• Thedataforonevariablearediscontinuous(non‐numericalorcategories).• Thedataforthedependentvariableareusuallyintheformofcounts,proportionsor

percentages.• Piegraphsaregoodforvisualimpactandshowingrelativeproportions.• Theyarenotsuitablefordatasetswithalargenumberofcategories.

LineGraphsareusedwhenonevariable(theindependentvariable)affectsanother,thedependentvariable.Linegraphscanbedrawnwithorwithoutameasureofspread(errorbars).Importantfeaturesoflinegraphsinclude:

• Thedatamustbecontinuousforbothvariables.• Thedependentvariableisusuallythebiologicalresponse.• Theindependentvariableisoftentimeortheexperimentaltreatment.• Incaseswherethereisanimpliedtrend(e.g.onevariableincreaseswiththeother)

alineofbestfitisusuallyplottedthroughthedatapointstoshowtherelationship.• Iffluctuationsinthedataarelikelytobeimportant(e.g.withclimateandother

environmentaldata)thedatapointsareusuallyconnecteddirectly(point‐to‐point).• Linegraphsmaybedrawnwithameasureoferror.Thedataarepresentedas

points(thecalculatedmeans),withbarsaboveandbelow,indicatingameasureofvariabilityorspreadinthedata(e.g.standarderror,standarddeviationor95%confidenceintervals).

• Wherenoerrorvaluehasbeencalculated,thescattercanbeshownbyplottingtheindividualdatapointsverticallyaboveandbelowthemean.Byconvention,barsarenotusedtoindicatetherangeofrawvaluesinadataset.

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Whenyouaretryingtocomparemultipledatasets,itismostusefultodosoonthesameaxes:

• Ifthetwodatasetsusethesamemeasurementunitsandasimilarrangeofvaluesfortheindependentvariables,onescaleonthey‐axisisused.

• Ifthetwodatasetsusedifferentunitsand/orhaveaverydifferentrangeofvaluesfortheindependentvariable,twoscalesforthey‐axisareused(seeexampleprovided).Thescalescanbeadjustedifnecessarytoavoidoverlappingplots.

• Thetwocurvesmustbedistinguished(usealegend!)

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Kitegraphsareidealforrepresentingdistributionaldata(e.g.abundancealonganenvironmentalgradient).Theyareelongatedfiguresdrawnalongabaseline.Importantfeaturesofkitegraphsinclude:

• Eachkiterepresentschangesinspeciesabundanceacrossalandscape.Theabundancecanbecalculatedfromthekitewidth.

• Theyofteninvolveplotsformorethanonespecies;thismakesthemgoodforhighlightingprobabledifferencesinhabitatpreferencesbetweenspecies.

• Athinlineonakitegraphrepresentsspeciesabsence(zerovalue).

• Theaxescanbereverseddependinguponpreference.

• Kitegraphsmayalsobeusedtoshowchangesindistributionwithtime,forexamplewithdailyorseasonalcyclesofmovement.

Note–MSExcelwillonlydoakitegraphifyouhavetheMerlinAdd‐In.(PConly)ScatterGraphsareacommonwaytodisplaycontinuousdatawherethereisarelationshipbetweentwointerdependentvariables.Importantfeaturesofscattergraphsinclude:

• Thedataforthegraphmustbecontinuousforbothvariables.• Thereisnoindependent(manipulated)variable,butthevariablesareoften

correlated,i.e.theyvarytogetherinsomepredictableway.• Scattergraphsareusefulfordeterminingtherelationshipbetweentwovariables.• Thepointsonthegraphneednotbeconnected,butalineofbestfitisoftendrawn

throughthepointstoshowtherelationshipbetweenthevariables.o Thismaybedrawnbyeyeorcomputer‐generated.

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