Quantifying the actual number of addicted individuals has proven to be a complex and nuanced task, particularly because of difficulties with incomplete or biased sampling.
Colorimetry techniques can be biased by color changes in test strips (from airborne or finger borne contamination, perhaps) or interference (e.g., tinting contaminants) with light source or the light sensor.
It is of particular interest that the memory of an eyewitness can become compromised by other information, such that an individual's memory becomes biased.
