Statistics for Environmental Engineers

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Table 6.1 gives the 121 averages of ten consecutive observations that can be calculated from the historical data. The ten-day moving averages are plotted in Figure 6.2. Figure 6.3 is a reference distribution for these averages. Six of the 121 ten-day averages are as low as 6.74. About 95% of the ten-day averages are larger than 6.74. Having only 5% of past ten-day averages at this level or lower indicates that the river pH may have changed.


Data Used to Plot Figure 6.1 and the Associated External Reference Distributions


6.79


6.84


6.85


6.47


6.67


6.76


6.75


6.72


6.88


6.83


6.65


6.77


6.92


6.73


6.94


6.84


6.71


6.88


6.66


6.97


6.63


7.06


6.55


6.77


6.99


6.70


6.65


6.87


6.89


6.92


6.74


6.58


6.40


7.04


6.95


7.01


6.97


6.78


6.88


6.80


6.77


6.64


6.89


6.79


6.77


6.86


6.76


6.80


6.80


6.81


6.81


6.80


6.90


6.67


6.82


6.68


6.76


6.77


6.70


6.62


6.67


6.84


6.76


6.98


6.62


6.66


6.72


6.96


6.89


6.42


6.68


6.90


6.72


6.98


6.74


6.76


6.77


7.13


7.14


6.78

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