4
Figures
Figure 1. Normal Distribution With Z-scores and Percentiles
Displayed
–4 –3
0.1
1 in
1,000
1 in
100
0.01
1 in
10,000
1 5
1 in
20
1 in
10
10 2030 50 7080 90 95 99
–2
–1
0
Z-Score
Percentile
Probability that a healthy individual
has abnormal results
1 2 3 4
Percentile can be interpreted as the probability that a healthy individual has an abnormal result
(i.e., the false positive rate).
e 5th and 95th percentile limits (–1.645 and +1.645 z-scores) of the healthy population can be used
to identify individuals with unusually low or high results, respectively.
