Business Statistics, 3e by Ken Black Chapter 11 Discrete Distributions Analysis of Variance & Design of Experiments Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-1 Learning Objectives • Understand the differences between various experimental designs and when to use them. • Compute and interpret the results of a one-way ANOVA. • Compute and interpret the results of a random block design. • Compute and interpret the results of a two-way ANOVA. • Understand and interpret interaction. • Know when and how to use multiple comparison techniques. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-2 Introduction to Design of Experiments, #1 Experimental Design - a plan and a structure to test hypotheses in which the researcher controls or manipulates one or more variables. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-3 Introduction to Design of Experiments, #2 Independent Variable • Treatment variable is one that the experimenter controls or modifies in the experiment. • Classification variable is a characteristic of the experimental subjects that was present prior to the experiment, and is not a result of the experimenter’s manipulations or control. • Levels or Classifications are the subcategories of the independent variable used by the researcher in the experimental design. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-4 Introduction to Design of Experiments, #3 Dependent Variable - the response to the different levels of the independent variables. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-5 Three Types of Experimental Designs • Completely Randomized Design • Randomized Block Design • Factorial Experiments Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-6 Completely Randomized Design 1 Machine Operator 2 3 Valve Opening Measurements . . . . . . . . . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-7 Example: Number of Foreign Freighters Docking in each Port per Day Long Beach Houston New York New Orleans 5 2 8 3 7 3 4 5 4 5 6 3 2 4 7 4 6 9 2 8 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-8 Analysis of Variance: Assumptions • Observations are drawn from normally distributed populations. • Observations represent random samples from the populations. • Variances of the populations are equal. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-9 One-Way ANOVA: Procedural Overview H : o 1 2 3 k Ha: At least one of the means is different from the others MSC F MSE If F > If F F , reject H . F , do not reject H . c o c Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning o 11-10 One-Way ANOVA: Sums of Squares Definitions total sum of squares = error sum of squares + between sum of squares SST = SSC + SSE C nj X ji X j=1 i=1 where: n j X j X X ij X j 2 C 2 j 1 C nj 2 j 1 i 1 i particular member of a treatment level j = a treatment level C = number of treatment levels n j number of observations in a given treatment level X = grand mean X X j ij = mean of a treatment group or level individual value Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-11 Partitioning Total Sum of Squares of Variation SST (Total Sum of Squares) SSC (Treatment Sum of Squares) Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning SSE (Error Sum of Squares) 11-12 One-Way ANOVA: Computational Formulas X X X X 2 C SSC n j j j 1 C SSE nj nj SST j 1 i 1 MSC ij MSE X SSC df C C 1 2 j 1 i 1 C df C ij X j df E N C 2 df T N 1 where: i = a particular member of a treatment level j = a treatment level SSE C = number of treatment levels df n= MSC F MSE j E number of observations in a given treatment level X = grand mean X X = j ij column mean individual value Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-13 One-Way ANOVA: Preliminary Calculations New Orleans Long Beach Houston New York 5 7 4 2 2 3 5 4 6 8 4 6 7 9 8 3 5 3 4 2 T1 = 18 T2 = 20 T3 = 42 T4 = 17 n1= 4 n2 = 5 n3 = 6 n4 = 5 T = 97 N = 20 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-14 One-Way ANOVA: Sum of Squares Calculations 1 18 1 4 T: T n: n X : X j j j C 1 4.5 2 20 2 5 T n X 2 3 42 3 6 T n X 4.0 3 7.0 4 42 T 97 4 5 N 20 3.4 X 4.85 T n X 4 nj X j 1 i 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 5 7 4 2 2 3 5 4 6 8 4 ji 2 2 2 2 2 2 6 7 9 8 3 5 3 4 2 557.00 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-15 One-Way ANOVA: Sum of Squares Calculations C SSC n j j 1 X 2 j X [ 4 (4.5 4.85) 5 (4.0 4.85) 6 (4.7 4.85) 5 (3.4 4.85) 2 2 42.35 C nj SSE j 1 i 1 X ij X j 2 2 2 (5 4.5) (7 4.5) (4 4.5) (2 4.5) 2 2 2 2 (2 4.0) (3 4.0) (4 34 . ) (2 34 . ) 2 2 2 2 44.20 C nj SST j 1 i 1 X ij X 2 (5 4.85) (7 4.85) (4 4.85) (4 4.85) (2 4.85) 2 2 2 2 2 8655 . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-16 One-Way ANOVA: Mean Square and F Calculations df df df C C 1 4 1 3 N C 20 4 16 E T N 1 20 1 19 MSC MSE SSC df C SSE df 42.35 14.12 3 44.20 2.76 16 E MSC 14.12 F 512 . MSE 2.76 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-17 Analysis of Variance for the Freighter Example Source of Variancedf SS MS F Factor Error Total 3 16 19 42.35 44.20 86.55 14.12 2.76 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 5.12 11-18 A Portion of the F Table for = 0.05 F Denominator Degrees of Freedom 1 ... 15 16 17 .05, 3,16 Numerator Degrees of Freedom 1 2 3 4 5 6 7 8 9 161.45 199.50 215.71 224.58 230.16 233.99 236.77 238.88 240.54 ... ... ... ... ... ... ... ... ... 4.54 3.68 3.29 3.06 2.90 2.79 2.71 2.64 2.59 4.49 3.63 3.24 3.01 2.85 2.74 2.66 2.59 2.54 4.45 3.59 3.20 2.96 2.81 2.70 2.61 2.55 2.49 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-19 One-Way ANOVA: Procedural Summary Ho : 1 2 3 4 Ha : At least one of the means is different from the others If F > If F F 3.24, reject H . F 3.24, do reject H . 3 2 16 o c o c Since F = 5.12 > 1 Rejection Region Non rejection Region F 3.24, reject H . c o Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning F .05,9 ,11 3.24 Critical Value 11-20 MINITAB Output for the Freighter Example ANALYSIS OF VARIANCE Source df Factor 3 Error 16 Total 19 SS 42.35 44.20 86.55 MS 14.12 2.76 LEVEL Long B Houston New York NewOrlns N 4 5 6 5 Mean 4.500 4.000 7.000 3.400 StDev 2.082 1.581 1.789 1.140 Pooled StDev = 1.662 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning F 5.11 p 0.011 11-21 Excel Output for the Freighter Example Anova: Single Factor SUMMARY Groups Long Beach Houston New York New Orleans Count 4 5 6 5 ANOVA Source of Variation Between Groups Within Groups SS 42.35 44.2 Total 86.55 Sum Average Variance 18 4.5 4.3333 20 4 2.5 42 7 3.2 17 3.4 1.3 df 3 16 MS 14.117 2.7625 F P-value 5.1101 0.0114 F crit 3.2389 19 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-22 Multiple Comparison Tests An analysis of variance (ANOVA) test is an overall test of differences among groups. Multiple Comparison techniques are used to identify which pairs of means are significantly different given that the ANOVA test reveals overall significance. • Tukey’s honestly significant difference (HSD) test requires equal sample sizes • Tukey-Kramer Procedure is used when sample sizes are unequal. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-23 Tukey’s Honestly Significant Difference (HSD) Test MSE HSD q ,C,N-C n where: MSE = mean square error n = sample size q ,C,N-C = critical value of the studentized range distribution from Table A.10 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-24 Data for Demonstration Problem 11.1 PLANT (Employee Age) Group Means nj C=3 dfE = N - C = 12 1 29 27 30 27 28 2 32 33 31 34 30 3 25 24 24 25 26 28.2 5 32.0 5 24.8 5 MSE = 1.63 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-25 q Values for = .01 Number of Populations Degrees of Freedom 1 2 3 4 5 90 135 164 186 2 14 19 22.3 24.7 3 8.26 10.6 12.2 13.3 4 6.51 8.12 9.17 9.96 11 4.39 5.14 5.62 5.97 12 4.32 5.04 5.50 5.84 ... q 504 . .01,3,12 . . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-26 Tukey’s HSD Test for the Employee Age Data HSD q ,C , N C XX XX X X MSE 163 . 5.04 2.88 n 5 1 2 28.2 32.0 38 . 1 3 28.2 24.8 3.4 2 3 32.0 24.8 7.2 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-27 Tukey-Kramer Procedure: The Case of Unequal Sample Sizes HSD q ,C,N-C MSE 1 1 ( ) 2 nr ns where: MSE = mean square error n n q r sample size for s r = sample size for s = ,C,N-C th th sample sample = critical value of the studentized range distribution from Table A.10 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-28 Freighter Example: Means and Sample Sizes for the Four Ports Port Long Beach Houston New York New Orleans Sample Size 4 5 6 5 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning Mean 4.50 4.00 7.00 3.40 11-29 TukeyKramer Results for the Freighter Example Pair 1 and 2 Critical |Actual Difference Differences| 3.19 0.50 (Long Beach and Houston) 1 and 3 3.07 2.50 3.19 0.35 2.88 3.00 * 3.01 0.60 2.88 3.60 * (Long Beach and New York) 1 and 4 (Long Beach and New Orleans) 2 and 3 (Houston and New York) 2 and 4 (Houston and New Orleans) 3 and 4 (New York and New Orleans) *denotes significant at .05 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-30 Partitioning the Total Sum of Squares in the Randomized Block Design SST (Total Sum of Squares) SSE (Error Sum of Squares) SSC (Treatment Sum of Squares) SSR (Sum of Squares Blocks) Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning SSE’ (Sum of Squares Error) 11-31 A Randomized Block Design Single Independent Variable . Individual observations . Blocking Variable . . . . . . . . . . . . . . . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-32 Randomized Block Design Treatment Effects: Procedural Overview Ho : 1 2 3 k Ha : At least one of the means is different from the others MSC F MSE If F > If F F , reject H . F , do not reject H . c c o o Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-33 Randomized Block Design: Computational Formulas C SSC n ( X j X ) j 1 n SSR C ( X i 1 n n i X ) 2 2 SSE ( X ij X i X i X ) j 1 i 1 n n SST ( X ij X ) j 1 i 1 SSC MSC C 1 SSR MSR n 1 SSE MSE N n C 1 MSC F treatments MSE MSR F blocks MSE 2 2 df C df R df E df E C 1 n 1 C 1 n 1 N n C 1 N 1 where: i = block group (row) j = a treatment level (column) C = number of treatment levels (columns) n = number of observations in each treatment level (number of blocks - rows) X individual observation X treatment (column) mean X block (row) mean ij j i SSC sum of squares columns (treatment) SSR = sum of squares rows (blocking) SSE = sum of squares error SST = sum of squares total X = grand mean N = total number of observations Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-34 Randomized Block Design: Tread-Wear Example Speed Supplier Slow Medium Fast Block Means ( X ) i n=5 1 3.7 4.5 3.1 3.77 2 3.4 3.9 2.8 3.37 3 3.5 4.1 3.0 3.53 4 3.2 3.5 2.6 3.10 5 3.9 4.8 3.4 4.03 3.54 4.16 2.98 3.56 Treatment Means( X ) j N = 15 X C=3 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-35 Randomized Block Design: Sum of Squares Calculations (Part 1) C SSC n ( X j X ) j 1 2 5[(3.54 356 . ) (4.16 356 . ) (2.98 356 . ) 2 2 2 3484 . n SSR C ( X i 1 i X ) 2 3[(3.77 356 . ) (3.37 356 . ) (3.53 356 . ) (3.10 356 . ) (4.03 356 . )] 2 2 2 2 2 1549 . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-36 Randomized Block Design: Sum of Squares Calculations (Part 2) C n SSE ( X ij X j X i X ) j 1 i 1 2 (3.7 354 . 377 . 356 . ) (3.4 354 . 337 . 356 . ) 2 2 (2.6 2.98 310 . 356 . ) (3.4 2.98 4.03 356 . ) 0143 . 2 C n SST ( X ij X ) 2 2 j 1 i 1 (3.7 356 . ) (3.4 356 . ) (2.6 3.56) (3.4 356 . ) 2 2 2 2 5176 . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-37 Randomized Block Design: Mean Square Calculations SSC 3.484 MSC 1742 . C 1 2 SSR 1549 . MSR 0.387 n 1 4 SSE 0143 . MSE 0.018 N n C 1 8 MSC 1742 . F 96.78 MSE 0.018 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-38 Analysis of Variance for the Tread-Wear Example Source of VarianceSS df Treatment 3.484 Block 1.549 Error 0.143 Total 5.176 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning MS 2 4 8 14 F 1.742 0.387 0.018 96.78 21.50 11-39 Randomized Block Design Treatment Effects: Procedural Summary Ho: 1 2 3 Ha: At least one of the means is different from the others MSC 1742 . F 96.78 MSE 0.018 F = 96.78 > F .01,2,8 = 8.65, reject Ho. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-40 Randomized Block Design Blocking Effects: Procedural Overview Ho: 1 2 3 4 5 Ha: At least one of the blocking means is different from the others MSR .387 F 215 . MSE .015 F = 21.5 > F .01,4 ,8 = 7.01, reject Ho. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-41 Excel Output for Tread-Wear Example: Randomized Block Design Anova: Two-Factor Without Replication SUMMARY Suplier 1 Suplier 2 Suplier 3 Suplier 4 Suplier 5 Slow Medium Fast Count Sum 11.3 10.1 10.6 9.3 12.1 Average 3.7666667 3.3666667 3.5333333 3.1 4.0333333 Variance 0.4933333 0.3033333 0.3033333 0.21 0.5033333 5 17.7 5 20.8 5 14.9 3.54 4.16 2.98 0.073 0.258 0.092 3 3 3 3 3 ANOVA Source of Variation SS df MS F P-value F crit Rows 1.5493333 4 0.3873333 21.719626 0.0002357 7.0060651 Columns 3.484 2 1.742 97.682243 2.395E-06 8.6490672 Error 0.1426667 8 0.0178333 Total 5.176 14 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-42 Two-Way Factorial Design Column Treatment . . Row Treatment Cells . . . . . . . . . . . . . . . Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-43 Two-Way ANOVA: Hypotheses Row Effects: Ho: Row Means are all equal. Ha: At least one row mean is different from the others. Columns Effects: Ho: Column Means are all equal. Ha: At least one column mean is different from the others. Interaction Effects: Ho: The interaction effects are zero. Ha: There is an interaction effect. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-44 Formulas for Computing a Two-Way ANOVA R SSR nC ( X i 1 C i X ) 2 SSC nR ( X j X ) j 1 R df 2 C SSI n ( X ij X i X j X ) i 1 j 1 SSE ( X ijk X ij ) R C n i 1 j 1 k 1 C R n SST ( X ijk X ) c 1 r 1 a 1 SSR R 1 SSC MSC C 1 SSI MSI R 1 C 1 SSE MSE RC n 1 MSR 2 2 2 R df C df I df df E T R 1 C 1 where: n = number of observations per cell R 1 C 1 C = number of column treatments RC n 1 N 1 MSR MSE MSC MSE MSI MSE FR F F C I Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning R = number of row treatments i = row treatment level j = column treatment level k = cell member X X X X ijk ij i j = individual observation = cell mean = row mean = column mean X = grand mean 11-45 A 2 3 Factorial Design with Interaction Row effects Cell Means R1 R2 C1 C2 Column C3 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-46 A 2 3 Factorial Design with Some Interaction Row effects Cell Means R1 R2 C1 C2 Column C3 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-47 A 2 3 Factorial Design with No Interaction Row effects Cell Means R1 R2 C1 C2 C3 Column Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-48 A 2 3 Factorial Design: Data and Measurements for CEO Dividend Example Location Where Company Stock is Traded How Stockholders are Informed of Dividends Annual/Quarterly Reports Presentations to Analysts Xj NYSE AMEX 2 1 2 1 X11=1.5 2 3 1 2 X21=2.0 2 3 3 2 X12=2.5 3 3 2 4 X22=3.0 1.75 2.75 OTC Xi 4 3 4 2.5 3 X13=3.5 4 4 3 2.9167 4 X23=3.75 X=2.7083 N = 24 n=4 3.625 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-49 A 2 3 Factorial Design: Calculations for the CEO Dividend Example (Part 1) R SSR nC ( X i X ) 2 i 1 ( 4)( 3)[( 2.5 2.7083) 2 (2.9167 2.7083) 2 ] 10418 . C SSC nR ( X j X ) 2 j 1 ( 4)( 2)[(1.75 2.7083) 2 ( 2.75 2.7083) 2 ( 3.625 2.7083) 2 ] 14.0833 R C SSI n ( X ij X i X j X ) 2 i 1 j 1 4[(15 . 2.5 1.75 2.7083) 2 ( 2.5 2.5 2.75 2.7083) 2 ( 3.5 2.5 3.625 2.7083) 2 ( 2.0 2.9167 1.75 2.7083) 2 ( 3.0 2.9167 2.75 2.7083) 2 (3.75 2.9167 3.625 2.7083) 2 ] 0.0833 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-50 A 2 3 Factorial Design: Calculations for the CEO Dividend Example (Part 2) SSE ( X ijk X ij) R C n 2 i 1 j 1 k 1 (2 15 . ) (115 . ) (3 375 . ) (4 375 . ) 2 2 2 2 7.7500 C R n SST ( X ijk X ) 2 c 1 r 1 a 1 (2 2.7083) (1 2.7083) (3 2.7083) (4 2.7083) 2 2 2 2 22.9583 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-51 A 2 3 Factorial Design: Calculations for the CEO Dividend Example (Part 3) SSR 10418 . MSR 10418 . R 1 1 SSC 14.0833 MSC 7.0417 C 1 2 SSI 0.0833 MSI 0.0417 R 1 C 1 2 SSE 7.7500 MSE 0.4306 RC n 1 18 MSR 10418 . F R MSE 0.4306 2.42 MSC 7.0417 F C MSE 0.4306 16.35 MSI 0.0417 . F I MSE 0.4306 010 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-52 Analysis of Variance for the CEO Dividend Problem Source of VarianceSS df Row 1.0418 Column 14.0833 Interaction 0.0833 Error 7.7500 Total 22.9583 *Denotes MS 1 2 2 18 23 F 1.0418 2.42 7.0417 16.35* 0.0417 0.10 0.4306 significance at = .01. Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-53 Excel Output for the CEO Dividend Example (Part 1) Anova: Two-Factor With Replication SUMMARY NYSE ASE OTC Total AQReport Count 4 4 4 12 Sum 6 10 14 30 Average 1.5 2.5 3.5 2.5 Variance 0.3333 0.3333 0.3333 1 Presentation Count Sum Average Variance 4 8 2 0.6667 4 12 3 0.6667 4 15 3.75 0.25 8 14 1.75 0.5 8 22 2.75 0.5 8 29 3.625 0.2679 12 35 2.9167 0.9924 Total Count Sum Average Variance Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-54 Excel Output for the CEO Dividend Example (Part 2) ANOVA Source of Variation Sample Columns Interaction Within SS 1.0417 14.083 0.0833 7.75 Total 22.958 df 1 2 2 18 MS 1.0417 7.0417 0.0417 0.4306 F P-value F crit 2.4194 0.1373 4.4139 16.355 9E-05 3.5546 0.0968 0.9082 3.5546 23 Business Statistics: Contemporary Decision Making, 3e, by Black. © 2001 South-Western/Thomson Learning 11-55
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