STATISTICS 2MA3

TEST #2 - 2001-03-01

Instructions

Aids permitted: any calculators, any tables and one sheet of notes (8.5" x 11", one side only).

Questions

1. The following data show diameter at breast height (dbh) in cm and total height (htt) in m for 10 old-growth Douglas fir on Vancouver Island. Compute the correlation coefficient. Display the data on an appropriate graph. Discuss your conclusions.

dbh:

31.75

50.55

77.03

56.90

98.99

58.42

34.29

57.91

39.37

52.07

htt:

23.2

36.5

40.2

33.5

41.4

37.1

28.8

34.2

30.3

36.7

2. Define the following terms: Sensitivity, Specificity, Predictive Value Positive, Risk Ratio, Odds Ratio. Compute each one for the following example.

The table below shows the number of subjects testing positive (diastolic blood pressure increased by 10 mm Hg or more following stimulating activity) by a manual method (assumed to be the "true" measure) and a new automated method.

manual

automated

< 10

>= 10

< 10

51

7

³ 10

15

6

Is this study prospective, retrospective, or cross-sectional?

3. If random variables X1, X2 each have the same mean m, but s1 = 5, s2 = 12, and r = 0.6, find the mean and variance of X1 - X2.

4. A paper published in the 1930s reported that a mean temperature was 28° F, and the standard deviation was 9°. Convert these values to °C. [Note: °C = (°F - 32)/1.8]

5. An airline knows that the weights of its passengers varies with mean 65 kg and standard deviation 9 kg. The plane has 100 seats and is always full. What is the probability that the total weight of 100 passengers will exceed 6600 kg? What is the probability that the total weight will exceed 6600 kg on more than 2 out of 10 flights? State any assumptions you make.