Introductory Biostatistics

Example 3.2 What is the probability of obtaining azvalue between
1 and
1? We have

Prð
 1 aza 1 Þ¼Prð
 1 aza 0 ÞþPrð 0 aza 1 Þ

¼ 2 Prð 0 aza 1 Þ

¼ð 2 Þð 0 : 3413 Þ

¼ 0 : 6826

which confirms the number listed in Figure 3.4. This area is shown graphically
in Figure 3.6.

Example 3.3 What is the probability of obtaining azvalue of at least 1.58?
We have

Prðzb 1 : 58 Þ¼ 0 : 5 
Prð 0 aza 1 : 58 Þ

¼ 0 : 5 
 0 : 4429

¼ 0 : 0571

and this probability is shown in Figure 3.7.

Example 3.4 What is the probability of obtaining azvalue of
0 :5 or larger?
We have

Prðzb
 0 : 5 Þ¼Prð
 0 : 5 aza 0 ÞþPrð 0 azÞ

¼Prð 0 aza 0 : 5 ÞþPrð 0 azÞ

¼ 0 : 1915 þ 0 : 5

¼ 0 : 6915

and this probability is shown in Figure 3.8.

Figure 3.6 Graphical display for Example 3.2.

126 PROBABILITY AND PROBABILITY MODELS