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Biostatistics

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EXERCISES 127<br />

Data:<br />

C1:-3-2-10123<br />

Dialog<br />

box:<br />

Session<br />

command:<br />

Calc Probability Distributions Normal MTB > CDF C1;<br />

SUBC> Normal 0 1.<br />

Choose Cumulative probability. Choose Input column<br />

and type C1. Click OK.<br />

Output:<br />

Cumulative Distribution Function<br />

Normal with mean<br />

deviation 1.00000<br />

0 and standard<br />

x P( X < x)<br />

3.0000 0.0013<br />

2.0000 0.0228<br />

1.0000 0.1587<br />

0.0000 0.5000<br />

1.0000 0.8413<br />

2.0000 0.9772<br />

3.0000 0.9987<br />

FIGURE 4.7.4<br />

MINITAB calculation of cumulative standard normal probabilities.<br />

EXERCISES<br />

4.7.1 For another subject (a 29-year-old male) in the study by Diskin et al. (A-11), acetone levels were<br />

normally distributed with a mean of 870 and a standard deviation of 211 ppb. Find the probability that<br />

on a given day the subject’s acetone level is:<br />

(a) Between 600 and 1000 ppb<br />

(b) Over 900 ppb<br />

(c) Under 500 ppb<br />

(d) Between 900 and 1100 ppb<br />

4.7.2 In the study of fingerprints, an important quantitative characteristic is the total ridge count for the<br />

10 fingers of an individual. Suppose that the total ridge counts of individuals in a certain population<br />

are approximately normally distributed with a mean of 140 and a standard deviation of 50. Find the<br />

probability that an individual picked at random from this population will have a ridge count of:<br />

(a) 200 or more<br />

(b) Less than 100

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