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Comparison of Sample Statistics with Parameters

Compares the sample statistics with parameters expected for a normal distribution. Since the mean and standard deviation were fitted from the data, they tell us nothing. The median 4.808) is slightly less than the mean (4.844), but the skewness coefficient (0.14) is fairly close to the value (0.00 that would be expected in a symmetric normal distribution. The sample quartiles (4.700 and 4.983) are nearly what we expect for a normal distribution using the 25th and 75th percentiles (xx ± 0.675s). There are no outliers, as the smallest Kiss (4.520 grams) is 2.01 standard deviations below the mean, while the largest Kiss (5.103 grams) is 1.61 standard deviations above the mean.
TABLE 15.18 Sample vs. Normal
Statistic Kiss Weight If Normal
Mean 4.844 4.844
Standard Deviation 0.161 0.161
Quartile 1 4.700 4.735
Median 4.808 4.844
Quartile 3 4.983 4.952
Skewness 0.14 0.00

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? Certainty

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 handheld 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, and Descent). Research question: At α = .05, is the cockpit noise level independent of flight phase? (Data are from Capt. Robert E. Hartl, retired.) Noise

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