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ANOVA Prof. Ivan Balducci FOSJC / Unesp Suposições necessárias para o Modelo ANOVA

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Modelo: One-way ANOVA The one-way ANOVA fits data to this: Y i,j = grand mean + group effect + ε i,j Y i,j = the value of the i th subject of the j th group Group effect = the difference between the means of population i and the grand mean Each ε i,j is a random value from a normally distributed population with a mean of 0

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Y ij = + j + eij data = fit + resíduo Modelo: One-way ANOVA Fit = média geral + efeito tratamento

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DATA = FIT + RESIDUALS Em qualquer modelo ANOVA vale sempre a relação acima: DATA = FIT + RESIDUALS ANOVA 1 way ANOVA 2 way ANOVA 3 way NESTED ANOVA ANCOVA SPLIT PLOT ANOVA RM ANOVA RANDOMIZED BLOCK ANOVA

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Checking the Analysis of Variance Assumptions 1. To check for normality, use the normal probability plot for the residuals. The residuals should exhibit a straight-line pattern, sloping upward to the right. 2.To check for equality of variance, use the residuals versus fit plot. The plot should exhibit a random scatter, with the same vertical spread around the horizontal zero error line.

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ANOVA Assumptions 1.The observations within each population are normally distributed with a common variance 2. 2.Assumptions regarding the sampling procedures are specified for each design. 1.The observations within each population are normally distributed with a common variance 2. 2.Assumptions regarding the sampling procedures are specified for each design. Remember that ANOVA procedures are fairly robust when sample sizes are equal and when the data are fairly mound-shaped.

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Diagnostic Tools 1.Normal probability plot of residuals 2.Plot of residuals versus fit or residuals versus variables 1.Normal probability plot of residuals 2.Plot of residuals versus fit or residuals versus variables Many computer programs have graphics options that allow you to check the normality assumption and the assumption of equal variances.

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Residuals The analysis of variance procedure takes the total variation in the experiment and partitions out amounts for several important factors. residualexperimental errorThe leftover variation in each data point is called the residual or experimental error. normalIf all assumptions have been met, these residuals should be normal, with mean 0 and variance 2.

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If the normality assumption is valid, the plot should resemble a straight line, sloping upward to the right. If not, you will often see the pattern fail in the tails of the graph. If the normality assumption is valid, the plot should resemble a straight line, sloping upward to the right. If not, you will often see the pattern fail in the tails of the graph. Normal Probability Plot

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If the equal variance assumption is valid, the plot should appear as a random scatter around the zero center line. If not, you will see a pattern in the residuals. If the equal variance assumption is valid, the plot should appear as a random scatter around the zero center line. If not, you will see a pattern in the residuals. Residuals versus Fits

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Key Concepts Checking the Analysis of Variance Assumptions 1. To check for normality, use the normal probability plot for the residuals. The residuals should exhibit a straight-line pattern, sloping upward to the right. 2.To check for equality of variance, use the residuals versus fit plot. The plot should exhibit a random scatter, with the same vertical spread around the horizontal zero error line.

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Normalidade dos resíduos Homogeneidade dos resíduos Termos que devem ser familiares

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Residuals and Residual Plots Most likely a linear regression will not fit the data perfectly. The residual (e) for each data point is the ________________________.

Residuals and Residual Plots Most likely a linear regression will not fit the data perfectly. The residual (e) for each data point is the ________________________.

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