For disease screening, a cutoff range that brings medical attention is established based on large data statistical analysis. A widely accepted definition for a cutoff range above the normal population is: "the interval between the cumulative 99th percentile of the normal population and the 5th percentile of disorder ranges of the same marker".
a) Based on the following data (normal population range and disorder range), determine the cutoff range for fatty acid C18:1.
|
Marker
|
|
Percentile values
|
|
C18:1 (pmol/L)
|
N
|
1%
|
5%
|
10%
|
50%
|
90%
|
99%
|
|
normal population
|
84
|
0.49
|
|
|
1.2
|
|
2.5
|
|
Disorder population
|
39
|
0.80
|
1.9
|
2.3
|
5.0
|
14
|
21
|
b) Discuss the consequences in terms of Type I or Type II errors if the cutoff range is changed by using i) the 1st percentile or ii) the 10th percentile of the disorder ranges while keeping the 99th percentile from normal population unchanged.