# Statistics for Environmental Engineers

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0

0

0

0

0

1 / 8

0

1

1 —

1

-1

-1

-1

1

1

1.1627

0

0

0

0

0

0

0

1 /8

-1

1

1

-1

1

-1

-1

1

3.4258

which

gives:

b0

= 1/8( 1.0472 + 3.2770 +

••• +

1.1627 + 3.4258

=

2.2278

b1 = 1/8(-1.0472 +3.2770 — 1.0805 + 3.4335 — 1.0817 + 3.3140 — 1.1627 + 3.4258) = 1.1348 b2 = 1/8(-1.0472 — 3.2770 + 1.0805 + 3.4335 — 1.0817 — 3.3140 + 1.1627 + 3.4258) = 0.0478

and so on.

The estimated coefficients are:

b0 = 2.2278 b1    = 1.1348    b2    = 0.0478    b3    = 0.0183

b12 = 0.0192    b13    = -0.0109    b23    = 0.0004    b123    = -0.0115

The subscripts indicate which factor or interaction the coefficient multiplies in the model. Because we are working with coded variables, b0 is the average of the observed values. Intrepreting b0 as the intercept where all x’s are zero is mathematically correct, but it is physical nonsense. Two of the factors are discrete variables. There is no method between A and B. Using half the amount of PMA preservative (i.e., x2 = 0) would either be effective or ineffective; it cannot be half-effective.

Скачать в pdf «Statistics for Environmental Engineers»