# Statistics for Environmental Engineers

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Example 7.1

Twenty replicate samples from five stations were counted for plankton, with the results given in Table 7.2. The computed averages and variances are in Table 7.3. The computed means and variance

on the original data show that variance is not uniform; it is ten times larger at station 5 than at

2

station 1. Also, the variance increases as the average increases and sy seems to be proportional to y. This indicates that a square root transformation may be suitable. Because most of the counts

Station 2

Station 3

Station 4

Station 5

0    48    12    16 0    1    2    3    4

Station 1

0 10

0

10

ш

з

O-

CD

10

10

0

Plankton Count    / Count + 0.5

FIGURE 7.3 Original and transformed plankton counts.

TABLE 7.4

Eight Replicate Measurements on Bacteria at Three Sampling Stations

y = Bacteria/100 mL    x = log10(Bacteria/100 mL)

 1 2 3 1 2 3 27 225 1020 1.431 2.352 3.009 11 99 136 1.041 1.996 2.134 48 41 317 1.681 1.613 2.501 36 60 161 1.556 1.778 2.207 120 190 130 2.079 2.279 2.114 85 240 601 1.929 2.380 Скачать в pdf «Statistics for Environmental Engineers» P. M. Berthouex, L. C. BrownISBN 1-56670-592-4Метки учебные пособия