During 1963 and 1964, an experiment was carried out in France; its design differed somew...

During 1963 and 1964, an experiment was carried out in France; its design differed somewhat from those of the previous two problems. A 1500-km target area was selected, and an adjacent area of about the same size was designated as the control area; 33 ground generators were used to produce silver iodide to seed the target area. Precipitation was measured by a network of gauges for each suitable “rainy period,” which was defined as a sequence of periods of continuous precipitation between dry spells of a specified length. When a forecaster determined that the situation was favorable for seeding, he telephoned an order to a service agent, who then opened a sealed envelope that contained an order to actually seed or not. The envelopes had been prepared in advance, using a table of random numbers. The following table gives precipitation (in inches) in the target and control areas for the seeded and unseeded periods.

a. Analyze the data, which are listed in chronological order, to see if there is an effect of seeding.

b. The analysis done by the French investigators used the square root transformation in order to make normal theory more applicable. Do you think that taking the square root was an effective transformation for this purpose?

c. Reflect on the nature of this design. In particular, what advantage is there to using the control area? Why not just compare seeded and unseeded periods on the target area?