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15.18 Sixty-four students in an introductory college economics class were asked how many credits they

had earned in college, and how certain they were about their choice of major. Research question:

At α = .01, is the degree of certainty independent of credits earned?

H0 = The degree of certainty is not independent of the credits earned

H1 = The degree of certainty is independent of the credits earned

Significance level=.01

Chi-square value = a (f – e)^2 /e =14.76

Critical value of chi-square corresponding to dof = (3 – 1)(3 – 1) = 4 and a = .01 is 13.28

Reject H0 if chi-square obtained > 13.28

Since 14.76 > 13.28, reject the H0; accept Ha.

degree of certainty is independent of credits earned.

15.22 A student team examined parked cars in four different suburban shopping malls. One hundred vehicles

were examined in each location. Research question: At α = .05, does vehicle type vary by

mall location? (Data are from a project by MBA students Steve Bennett, Alicia Morais, Steve

Olson, and Greg Corda.)

H0: Vehicle type / mall location independent

H1: Vehicle type / mall location dependent

(44-48.25)2/48.25 +(9-11.5)2/11.5 = 24.53

Dof =(5-1)(4-1)=12

reject H0 if p-vlaue <0.05

If X has chi-square distr w/ 12 dof then,

p-value = P(X>24.53) = .01721

Since p-value > 0.05; reject H0

Yes, a = .01 vehicle type does vary by location

15.24 High levels of cockpit noise in an aircraft can damage the hearing of pilots who are exposed to this hazard for many hours. A Boeing 727 co-pilot collected 61 noise observations using a hand held sound meter. Noise level is defined as “Low” (under 88 decibels), “Medium” (88 to 91 decibels), or “High” (92 decibels or more). There are three flight phases (Climb, Cruise, Descent). Research question: a. At a = .05, is the cockpit noise level independent of flight phase? (Data are from Capt. Robert E. Hartl, retired.)

H0: Noise level / flight phase independent

H1: Noise level / flight phase...