8127/frame/fm

 
AB
P
rints and blood spatt
er
. A ser
ies of
e
xp
er
iments w
er
e p
er
for
med t
o
see if
it
was possible t
o
t
el
l w
hic
h was deposit
ed 
fi
rst,
the pr
int or the blood.
I
n
this
par
ticular var
iation,
blood was 
fi
rst spatt
er
ed ont
o
a subst
ra
te
, a palm pr
int applied
on t
o
p of
it,
and then black po
w
der used t
o
v
isualiz
e the lat
ent pr
int.
P
anels 
A and
B r
epr
esent r
esults fr
om the same exp
er
imental c
o
nditions,
but p
er
for
med at
differ
ent times.
P
anel 
A:
The r
idge detail clearly r
uns c
o
ntin
uously o
ver the blood
dr
oplet.
P
anel B:
Ther
e is no ob
vious c
oher
ent patt
er
n t
o
the po
w
der on the blood
dr
op
. Exp
er
ienc
ed analysts w
ho belie
ve
d that the
y c
ould r
eliably det
er
mine
w
h
ether the blood or the pr
int was deposit
ed 
fi
rst inc
or
re
ct
ly c
o
ncluded that,
for
the e
xample in P
anel B
, the pr
int was deposit
ed befor
e the blood.
A
t t
rial,
the defense e
xp
er
t pr
esent
ed the r
esults of
his e
xp
er
imentation
and t
esting
. H
e t
esti
fi
ed that it was not p
ossible t
o
t
ell,
at least base
d on the
cr
it
er
ia pr
offer
ed,
w
hic
h mig
ht ha
ve
been deposit
ed 
fi
rst,
a pr
int or some blood
spatt
er
. H
e offer
ed t
o
let the Oklahoma analyst tak
e the t
est.
This offer was
declined b
y the pr
osecut
o
r on behalf
of
the analyst.
This case pr
o
vides a useful lesson in the ne
cessit
y of
ac
tual
ly p
er
for
ming
validation e
xp
er
iments r
ather than blind
ly ac
ce
pting c
o
n
ventional w
isdom that
has been passed do
w
n
thr
oug
h or
al t
radition 
—
e
ven if
it is taug
ht in a class
at the FBI.
8127/frame/ch09 Page 227 Friday, July 21, 2000 11:44 AM

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228
Principles and Practice of Criminalistics
correct result. Reliability can be understood in terms of 
 
precision
— a reliable
result is one that can be reproduced within defined quantitative or qualitative
limits. The term 
 
validation
is commonly understood to pertain to studies
that help us ascertain both the validity and reliability of our results.
 
4.
Is Validation Required?
We cannot leave the subject of validation without emphasizing that its pri-
mary utility is to the analyst and the laboratory that is performing the work.
Validation establishes the capabilities and limitations of the system, and
builds a body of work from which practitioners can learn when variations
are explainable and when they indicate a real difference. The greatest utility
of validation studies is in providing the practitioner doing the work with
information that will assist in the interpretation of difficult samples. Valida-
tion studies are essential — for the field, for individual laboratories, and, in
the form of proficiency testing, for individuals. This is simply good science
and contributes to a solid foundation for performing work and interpreting
the results. Nevertheless, a lack of validation on some level does not, 
 
a priori
,
invalidate a particular analysis. However, the fewer challenges to which a
particular system has been subjected, the more assumptions that must be
made about the result of a particular test, and the weaker any conclusions
about the results must be.
 
C.
Quality Assurance and Quality Control
A list of references that address general scientific and also forensic-specific
quality assurance issues are provided following the general reference list for
this chapter.
 
1.
Quality Assurance
 
Quality assurance
guidelines, usually found in a 
 
quality manual
, define all
the aspects of a program that are necessary to ensure a minimum standard
of operation. These guidelines encompass everything from laboratory safety,
to personnel requirements, to documentation of method reliability. Both
fieldwide and in-house validation studies contribute specific information
upon which the procedures and protocols portion of the quality assurance
program is based.