Statistics for Environmental Engineers

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In practice, such a complex experiment would be designed in consultation with a statistician, in which case the method of data analysis is determined by the experimental design. The investigator will have no need to guess which method of analysis, or which computer program, will suit the data. As a corollary, we also recommend that happenstance data (data from unplanned experiments) should not be subjected to analysis of variance because, in such data sets, randomization will almost certainly have not been incorporated.

Dioxin Case Study Results


The ANOVA calculations were done on the natural logarithm of the concentrations because this transformation tended to strengthen the assumption of constant variance.


The results shown in Table 26.2 are the complete variance decomposition, specifying all sum of squares (SS) and degrees of freedom (df) for the main effects of the four factors and all interactions between the four factors. These are produced by any computer program capable of handling a four-way ANOVA


Variance Decomposition of the Dioxin/Furan Incinerator Emission Data


Source of Variation


SS


df


MS


F


S


18.3423


1


18.3423


573


CL


54.5564


4


13.6391


426


DF


11.1309


1


11.1305


348


DF x CL


22.7618


4


5.6905


178


S x P


9.7071


3


3.2357


101


P


1.9847


3


0.6616


21


DF x P


1.1749


3

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