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

More documents

Recommendations

Info

The next example shows the help supplied for theconfidence interval function.Example: Excel 2000 Confidence Function“CONFIDENCEReturns the confidence interval for apopulation mean. The confidence interval is arange on either side of a sample mean. Forexample, if you order a product through themail, you can determine, with a particular levelof confidence, the earliest and latest theproduct will arrive.” [emphasis mine]The material emphasized, is, of course, a basicmisstatement of the meaning of a confidence interval.A last example displays the help given for thestandard deviation function.Example: Excel 2000 STDEV Function“STDEVEstimates standard deviation based on asample. The standard deviation is a measureof how widely values are dispersed from theaverage value (the mean).(snip...)Remarks(snip...)The standard deviation is calculated using the"nonbiased" or "n-1" method.STDEV uses the following formula:∑∑n x 2 – x⎝⎛ ⎠⎞2------------------------------------------------nn ( – 1)This help item introduces a new term, nonbiased,but that is the least of the difficulties here. (And, ofcourse, the standard deviation given here is not unbiasedfor the population standard deviation under any set ofassumptions that I know of!) More importantly, theformula given, the so-called “computing formula,” iswell-known to be a very poor way to compute a standarddeviation. We return to this below.Excel is especially deficient in its statisticalanalysis when some of the data are missing.✔Excel Makes Selecting Predictor Variables InRegression Especially Difficult When DataMissingAs an example, here is a simple paired dataset withsome of the data missing (NA= not available ormissing):PrePost1 1NA 23 34 NA5 56 67 78 89 9Here is the output of the paired data analysis of thesedata with the Excel Data Analysis Toolpack:t-Test: Paired Two Sample for MeansVariable 1 Variable 2Mean 5.375 5.125Variance 7.125 8.410714286Observations 8 8Pearson Correlation 1Hypothesized Mean Difference 0df 7t Stat -1P(T
Computing Algorithms for Basic Statistics✔Excel Uses Poor Algorithms To Find TheStandard Deviation (See Help screen forSTDEV shown above)Get the Right Tool for the Job!✔✔Excel Defines The First Quartile To Be TheOrdered Observation At Position (n+3)/4Excel Does Not Treat Tied ObservationsCorrectly When Ranking✔Regression Computations Are Often ErroneousDue To Poor Algorithms (See below)In addition Excel, usually displays many more digitsthan appropriate. (See histogram and paired t-test outputshown above.)Finally, Excel has major and documenteddifficulties with its regression procedures.Regression in Excel✔✔✔✔✔✔Does Not Treat Zero-Intercept ModelsCorrectlySometimes Gets Negative Sums Of SquaresDoes Not Handle Multicollinearity CorrectlyComputes Standardized Residuals Incorrectly!Displays Normal Probability Plots That AreCompletely Wrong!Makes Variable Selection Very DifficultReferencesFriends Don’t Let FriendsUse Excel for Statistics!Allen, I. E. (1999), “The Role of Excel forStatistical Analysis”, Making Statistics MoreEffective in Schools of Business 14th AnnualConference Proceedings, ed. A. Rao,Wellesley: http://weatherhead.cwru.edu/msmesb/In summary:Due to substantial deficiencies, Excel should not beused for statistical analysis. We should discouragestudents and practitioners from such use.The following pretty much sums it up:Callaert, H. (1999), “Spreadsheets and Statistics:The Formulas and the Words”, Chance, 12, 2,p. 64.Cleveland, W. S., Visualizing Data, 1993, HobartPress, Summit, NJCleveland, W. S., The Elements of Graphing Data,Revised Edition, 1994, Hobart Press, Summit,NJGoldwater, Eva, Data Analysis Group, AcademicComputing, University of Massachusetts,Using Excel for Statistical Data Analysis:Successes and Cautions, November 5, 1999,www-unix.oit.umass.edu/~evagold/excel.html10
Page 1 and 2: Stat-403/Stat-650 : Intermediate Sa
Page 3: Chapter 1Statistics - why the badim
Page 8 and 9: Problems With Using MicrosoftExcel
Page 12 and 13: Knusel, Leo, “On the Accuracy of
Page 14 and 15: The latter tool is but one of many
Page 16 and 17: Is It Practical To Use Excel For St
Page 22 and 23: Using Excel for StatisticsStatistic
Page 24 and 25: Using Excel for StatisticsTipsWarni
Page 26 and 27: Using Excel for Statistics2. Adding
Page 28 and 29: Using Excel for StatisticsThe field
Page 30 and 31: Using Excel for StatisticsIn this e
Page 32 and 33: Using Excel for Statisticsbehaves l
Page 34 and 35: Using Excel for StatisticsThe resul
Page 36 and 37: Using Excel for Statisticsare liste
Page 38 and 39: DFID Guides Introduction PageStatis
Page 40 and 41: DFID Guides Introduction Pagetel: +
Page 42 and 43: BIOMETRICSINFORMATIONIndex of Pamph
Page 44 and 45: Index of Pamphlet TopicsExperimenta
Page 46 and 47: Index of Pamphlet TopicsRegression2
Page 48 and 49: Chapter 6How do I interpret a p-val
Page 50 and 51: 2Type I error in the data exceeds w
Page 52 and 53: 4ssssssssssssssssssssssssssssssssss
Page 61 and 62:
Chapter 8The Insignificance ofStati
Page 63 and 64:
Statistical Signigicance TestingEco
Page 65 and 66:
Statistical Signigicance TestingThe
Page 67 and 68:
Statistical Significance Testingof
Page 69 and 70:
Statistical Significance Testingapp
Page 71 and 72:
Statistical Significance TestingBio
Page 73 and 74:
Statistical Significance TestingThe
Page 75 and 76:
Statistical Significance Testinginf
Page 77 and 78:
Statistical Significance TestingHom
Page 79 and 80:
Statistical Significance Testingsug
Page 81 and 82:
Statistical Significance Testingres
Page 83 and 84:
Statistical Significance TestingThe
Page 85 and 86:
http://www.npwrc.usgs.gov/resource/
Page 87 and 88:
http://www.npwrc.usgs.gov/resource/
Page 89:
Chapter 9Designing EnvironmentalFie
Page 102 and 103:
101
Page 104 and 105:
103
Page 106 and 107:
105
Page 108 and 109:
107
Page 110 and 111:
109
Page 112 and 113:
Chapter 10Power analysis in wildlif
Page 114 and 115:
113
Page 116 and 117:
115
Page 118 and 119:
117
Page 120 and 121:
119
Page 122 and 123:
121
Page 124 and 125:
123
Page 126 and 127:
125
Page 128 and 129:
127
Page 130 and 131:
129
Page 132 and 133:
131
Page 134 and 135:
133
Page 136 and 137:
135
Page 138 and 139:
137
Page 140 and 141:
139
Page 142 and 143:
141
Page 144 and 145:
143
Page 146 and 147:
145
Page 148 and 149:
147
Page 150 and 151:
Chapter 12Pseudo-replication revisi
Page 152 and 153:
151
Page 154 and 155:
153
Page 156:
155
show all

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

Create successful ePaper yourself

Delete template?

Save as template?