STATISTICAL EVALUATION OF BREATHALYZER FIELD

STATISTICAL EVALUATION OF BREATHALYZER FIELD
SIMULATOR TESTS: LACK OF INFLUENCE BY
RADIOFREQUENCY SIGNALS
"to "fc
Y. H. Caplan, Ph.D. ; and D. T. Yohman, M.P.A.
SYNOPSIS
A study of 18,943 consecutive Breathalyzer simulator
tests conducted on 95 Breathalyzer instruments (Models 800,
900, and 900A) over a 9-month period in the State of
Maryland confirmed the reliability of the Breathalyzer.
Statistical analysis revealed a normal distribution of
results
around
a
standard
0.100%
simulated
alcohol
concentration and only a 1:5000 probability that any test
result would exceed 0.110%.
INTRODUCTION
Since
its
invention,
the
Breathalyzer
has
been
challenged on many grounds.
Recently, the question of the
influence of radiofrequency (RF) signals on test results has
been raised causing the Smith and Wesson Company to issue a
customer advisory in the fall of 1982.
In the State of
Maryland, the standard procedure practiced when conducting
Breathalyzer tests is to first test the subject and then,
following the subject test and using the same ampoule, to
conduct a simulator (validation) test with a simulator
solution targeted at
0.100%.
Although many previous
experiences were sufficiently convincing that Breathalyzer
tests were accurate, the publicity afforded the alleged RF
problem necessitated an additional exhaustive study.
It is
argued that if RF signals were inadvertently affecting
subject tests, then on a statistical basis a similar effect
should be noted in the population of simulator tests
concomitantly conducted.
To this end, all field simulator
tests consecutively conducted over a 9-month period in the
State of Maryland were evaluated and the results presented
in this report.
*
Office of the Chief Medical Examiner, State of Maryland,
111 Penn St., Baltimore, Maryland 21201, USA.
** Maryland State Police.
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METHODS
Instrumentation
The Smith & Wesson Breathalyzer Models 800, 900 and
900A as manufactured by the
Smith & Wesson
Company
(G.O.E.C., Pittsburgh, Pennsylvania.), the Smith & Wesson
Electronics Company
(Eatontown,
New Jersey), and the
Stephenson Corporation (Eatontownand Red Bank, New Jersey)
and which were certified in the State of Maryland were used
in this study.
The Smith & Wesson breath alcohol Simulators Mark II
and IIA were used in conjunction with the Breathalyzer to
deliver a simulated breath sample corresponding to a
reference blood alcohol concentration.
The breath alcohol simulator (validation test) solution
was prepared in the field by a qualified maintenance
technician.
Ten milliliters of alcohol simulator stock
solution (77 ml absolute ethanol per liter) were measured
into a 500 ml volumetric flask and the flask filled to
500 ml with distilled water to produce a 0.100% simulated
alcohol concentration.
Certified Breathalyzer Solution as distributed
ampoules by the Smith & Wesson Company were used
conjunction with the testing.
in
in
Study of Validation Tests
As part of the regulator practice of conducting breath
tests in Maryland, a validation test is conducted following
every subject test.
This test is conducted using a
simulated breath alcohol solution known as the validation
test solution. In addition, this solution is used for other
operator and maintenance tests not conducted in conjunction
with a subject test.
The validation test solution is the
reference standard producing a simulated blood alcohol
concentration of 0.100%. All tests utilizing the simulator
are recorded in the Log of Tests for Alcohol Influence
Arrests and identified either as validation test, simulator
test
(operator),
or
simulator
test
(maintenance).
Validation tests were conducted following subject tests
using the same ampoule of Certified Breathalyzer Solution.
All
simulator
tests
(operator)
and
simulator
tests
(maintenance)
were
conducted
as
required
by
the
Toxicologist's Regulations.
Simulator test results of all 3 types were abstracted
from the Log of Tests for Alcohol Influence Arrests and
compared to 0.100%, the target value of the standard.
234
Paired test results were statistically evaluated using a
SPSS (Statistical Package for Social Science) program and an
IBM (370-158) Computer.
RESULTS AND DISCUSSION
The 18,943 simulator tests including validation tests
following
subjects,
simulator
tests
(operator),
and
simulator
tests
(maintenance)
were
conducted
on
95
Breathalyzer instruments used in the State of Maryland
during the 9-month period, January 1, 1982 to September 30,
1982.
If RF signals were causing erroneous readings on
subject tests,
then it would be expected that this
phenomenon would be observable in the simulator tests. The
statistical results are compiled in Table 1.
The target
value for all tests was 0.100%.
The data were normally
distributed with the mean, median, and mode being 0.098%,
0.099% and 0.100%, respectively, which is in excellent
agreement with the target value of 0.100%.
The field
tolerance for accuracy for these tests is plus or minus
0.010%. Figure 1 shows the frequency distribution histogram
for the 18,943 validation tests. Note that 50 of the 18,943
tests were below 0.090%, indicative of the fact that
potential deviation of the test is on the low side. Only 4
of
the
tests
were
above
0.110%,
indicative
of
an
approximately 1:5000 chance that a test result will exceed
0.110%. This is far below that which normally be expected
on a statistical basis. These 4 test results were reported
on 4 different instruments (2 Model 900's and 2 Model
900A's) consistent with a random phenomenon.
Of the total
18,943 tests administered,
5% were conducted on the
Model 800, 50% on the Model 900, and 45% on the Model 900A.
Since it is not possible to evaluate the actual subject test
results because there is no true or target value available
for comparison, the study of the simulator tests provides
the only valid basis for estimating the effect on actual
subject tests.
Table 1
Statistical Data on Validation Tests
Total Tests
18,943
Mean
Median
Mode
Range
S. D.
S. E.
0.098%
0.099%
0 .1 0 0 %
0.00 - 0 .2 0 %
0.0036%
0.00003%
235
DISCUSSION
Although RF signals have been reported to cause
interference and effect the results of tests using some
Model 900A Breathalyzer instruments in the laboratory, these
conditions were not found to exist in field testing
locations in Maryland.
The validation test data provide
further evidence that under practical conditions of use, it
is not probable that any subject test would deviate outside
the expected scientific range. The statistical data is, in
fact, a remarkable testament to the accuracy of the
Breathalyzer.
236