Regardless of how highly optimized a procedure may be, the weak link will be
a human being.  Errors are inevitable, even at a low incidence, due to a
lapse of vigilance.  Even bar codes have associated reading error rates,
though small.

Vigilance is defined as sustained attention.  Lapses of vigilance (i.e., the
vigilance decrement) are universal and usually can be observed within 20
minutes of beginning a task.  Lapses of vigilance are insidious, meaning
they happen without warning, without the observer being aware of them, and
unable to stop them.  Insidious is rooted in a word that means "to ambush."

As a cytotechnologist, I have looked into the reasons we miss abnormal cells
when screening Pap smears.  The vigilance decrement is near the top of the
most common reasons, though it's impossible to prove when there's no
tangible evidence to retrace.  It's a default conclusion.

When shown false negatives they have missed, cytotechnologists virtually
universally respond:

1)	I recognize those cells.
2)	I don't know how I missed them.
3)	I don't know what I can do to guarantee that I'll never miss such
cells again.

In fact, there is nothing they can do that will allow them to make such a
guarantee.  Such is likely the case with mislabeling errors in histology,
IMHO.

Gary Gill