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A ESCOLHA DO MÉTODO ESTATÍSTICO - SBPqO

A ESCOLHA DO MÉTODO ESTATÍSTICO - SBPqO

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“We have discussed the practice of using different data<br />

transformations within a 2-way ANOVA with our statistical adviser and<br />

he stated that this is not valid, since the comparisons are not then<br />

between data of the same type. Transformation is performed to deal<br />

with 1 or more of 3 problems: non-normality, non-homogeneity of<br />

variance and non-additivity. To my understanding, in a 2-way analysis,<br />

'individualized' transformations, while solving the first two problems,<br />

would work against the third requirement of ANOVA, that treatment<br />

effects are additive. For instance, data in which treatment effect was<br />

multiplicative rather than additive are appropriately transformed to<br />

logs, since the treatment effects then become additive. But these<br />

could not then be compared with data that had not been transformed<br />

because they already fulfilled the ANOVA requirements. You would be<br />

comparing oranges and bananas.”<br />

“Sorry about the confusion induced by my last set of comments on<br />

the statistics. I think there might be still some sort of problem there, in<br />

that your comparison of the 30-min plaque solid data is on a<br />

somewhat different basis from the other comparisons. But I will<br />

discuss it when I next see our statistical advisor. I suspect that I put<br />

the question to him in a misleading way, combined with a misinterpretation<br />

of your analysis.”<br />

46

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