Stat-403/Stat-650 : Intermediate Sampling and Experimental Design ...

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Problems With Using MicrosoftExcel for StatisticsJonathan D. Cryer(Jon-Cryer@uiowa.edu)Department of Statistics and Actuarial ScienceUniversity of Iowa, Iowa City, IowaJoint Statistical MeetingsAugust 2001, Atlanta, GAIn this talk I will illustrate Excel’s serious deficienciesin five areas of basic statistics:andGraphicsHelp ScreensComputing AlgorithmsTreatment of Missing DataExample: Excel Graphics With False ThirdDimension (taken from JSE!)The vast majority of Chart types offered by Excelshould NEVER be used!Our next example shows the graph-types available aspyramid charts. None of these choices shown belowrepresent good graphs! All but the last one display falsethird dimensions. In addition they all suggest stackeddisplays that are known to be poor ways to makecomparisons.Example: Pyramid ChartsRegressionWe begin with basic graphics.Good Graphs Should:✔✔✔Portray Numerical Information VisuallyWithout DistortionContain No Distracting Elements (e.g., no falsethird dimensions nor “chartjunk”)Label Axes (Scales) and Tick MarksAppropriately✔Have a Descriptive Title and/or Caption andLegend(References: Cleveland (1993, 1994) and Tufte(1983, 1990, 1997))However, Excel meets virtually none of thesecriteria. As our first example illustrates, Excel offersfalse third dimensions on the vast majority of its graphs.(Unfortunately, this example is taken from the Journalof Statistical Education.)(For the similar reasons, Excel’s column, cone, andcylinder charts don’t seem to have any redeemingfeatures either!)Scatterplots represent bread-and-butter graphs forvisualizing relationships between variables.Scatterplots Should Have:7✔✔✔Good Choice of AxesMeaningful LegendsNo False Third Dimensions
However, Excel’s default scatterplots leave much to bedesired. In the following example two data points havebeen covered up by the axis labels. Can you find them?And is the legend displayed to the right of the graphuseful? Note that there is no label for the horizontal axis.Example: Excel Default ScatterplotExample: Excel Histogram (stretchedvertically to read labels)Histograms are another basic statistical display.Histograms Should Have:✔✔✔✔✔✔No Meaningless GapsA Reasonable Choice of BinsAn Easy Way To Choose Or Adjust The BinsA Good Aspect RatioMeaningful Labels on AxesAppropriate Labels on Bin Tick MarksHowever, the next example shows a default histogramproduced by Excel. The bin labels are impossible toread, the aspect ratio is poor, the legend and horizontalaxis label are useless.Example: Excel Default HistogramIf we click on the graph and stretch it vertically, we canthen read the bin labels.The choice of class intervals or bins is ratherbizarre, the number of digits displayed is atrocious, andit is not at all clear what tick marks these labels apply to.In any software, the help screens should give usefuland accurate information. In particular:Help Screens Should:✔✔✔Not ConfuseGive Accurate Statistical InformationBe Helpful!However, Excel’s help for statistics is quite poor.Here is an example of the Help screen displayed whenyou do a two-sample t-test.Example: Excel 2000 Help Screen for theTwo-sample T-Test“t-Test: Two-Sample Assuming EqualVariances analysis toolThis analysis tool performs a two-samplestudent's t-test.This t-test form assumes that the means ofboth data sets are equal; it is referred to as ahomoscedastic t-test.You can use t-tests to determine whether twosample means are equal.”These sentences contain a number of basic errors.About the only value in them would be to ask yourstudents to critique them and locate the many errors!8
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Page 42 and 43: BIOMETRICSINFORMATIONIndex of Pamph
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Chapter 8The Insignificance ofStati
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Statistical Signigicance TestingEco
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