Statistics for Environmental Engineers

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Observ.


У1


У2


Observ.


У1


У2


i


5.88


5.61


16


5.70


5.96


2


5.64


5.63


17


4.90


5.65


3


5.09


5.12


18


5.40


6.71


4


6.04


5.36


19


5.32


5.67


5


4.66


5.24


20


4.86


4.34


6


5.58


4.50


21


6.01


5.57


7


6.07


5.41


22


5.55


5.55


8


5.31


6.30


23


5.44


6.40


9


5.48


5.83


24


5.05


5.72


10


6.63


5.23


25


6.04


4.62


11


5.28


5.91


26


5.63


4.62


12


5.97


5.81


27


5.67


5.70


13


5.82


5.19


28


6.33


6.58


14


5.74


5.41


29


5.94


5.94


15


5.97


6.60


30


6.68


6.09

12.3 Moving Averages. Use the first 20 duplicate observations in the Exercise 12.2 data set to construct an MA(4) moving average chart and an EWMA chart for Я = 0.6. Plot the next ten observations and decide whether the process has remained in control. Compare the purpose and performance of the charts.

FIGURE 12.2 Moving average (5-day) and exponentially weighted moving average (X = 0.5) charts for the single observations shown in the top panel. The mean level shifts up by 0.5 units from days 50-75, it is back to normal from days 76-92, it shifts down by 0.5 units from days 93-107, and is back to normal from day 108 onward.

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