Smokestack scrubbers. Particulate matter is a serious form of air pollution often arising from industrial production.

One way to reduce the pollution is to put a filter, or scrubber, at the end of the smokestack to trap the particulates.

An experiment to determine which smokestack scrubber design is best was run by placing four scrubbers of different designs on an industrial stack in random order.

Each scrubber was tested 5 times. For each run, the same material was produced, and the particulate emissions coming out of the scrubber were measured (in parts per billion).

A partially complete Analysis of Variance table of the data is shown here.
Sum of Degrees of Mean Source Squares Freedom Square F-ratio Treatment 81.2 Residual 30.8 Total 112.0

a) Calculate the mean square of the treatments and the mean square of the error.

b) Form the F-statistic by dividing the two mean squares.

c) The P-value of this F-statistic turns out to be 0.00000949. What does this say about the null hypothesis of equal means?

d) What assumptions have you made in order to answer part c?

e) What would you like to see in order to justify the conclusions of the F-test?

f) What is the average size of the error standard deviation in particulate emissions?