4.88. Cost of modifying a naval air base. A naval base is considering modifying or adding to its…

4.88. Cost of modifying a naval air base. A naval base is considering modifying or adding to its…

4.88.        Cost of modifying a naval air base. A naval base

is considering modifying or adding to its fleet of 48 standard aircraft. The final decision regarding the type and number of aircraft to be added depends on a comparison of cost versus effectiveness of the modified fleet. Consequently, the naval base would like to model the projected percentage increase y in fleet effectiveness by the end of the decade as a function of the cost x of modifying the fleet. A first proposal is the quadratic model

E(y) = β0 + β1x + β2×2

The data provided in the table were collected on 10 naval bases of similar size that recently expanded their fleets.

1                                                               1

where        y = Emotional distress

x1 = Experience (years)

x2 = 1 if exposed to chemical fire, 0 if not

(a)    What hypothesis would you test to determine whether the rate of increase of emotional dis- tress with experience is different for the two groups of firefighters?

(b)    What hypothesis would you test to determine whether there are differences in mean emo- tional distress levels that are attributable to exposure group?

(c)    Data for a sample of 200 firefighters were used to fit the complete model as well as the reduced

1   model, E(y) = β0 + β1×1 + β2×2. The results are  SSER = 795.23  and  SSEC = 783.90. Is

there sufficient evidence to support the claim

that the mean emotional distress levels differ for the two groups of firefighters? Use α = .05.

 

 

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