STATISTICAL EVALUATION OF BREATHALYZER FIELD SIMULATOR TESTS: LACK OF INFLUENCE BY

RADIOFREQUENCY SIGNALS

"to "fcY. H. Caplan, Ph.D. ; and D. T. Yohman, M.P.A.

SYNOPSISA 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%.

INTRODUCTIONSince 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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METHODSInstrumentation

The Smith & Wesson Breathalyzer Models 800, 900 and900A as manufactured by the Smith & Wesson Company(G.O.E.C., Pittsburgh, Pennsylvania.), the Smith & WessonElectronics Company (Eatontown, New Jersey), and theStephenson Corporation (Eatontown and 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 in ampoules by the Smith & Wesson Company were used in conjunction with the testing.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.

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Paired test results were statistically evaluated using a SPSS (Statistical Package for Social Science) program and an IBM (370-158) Computer.

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.

RESULTS AND DISCUSSION

Table 1Statistical Data on Validation Tests

Total Tests 18,943MeanMedianMode Range S. D. S. E.

0.098% 0.099% 0 .1 0 0 %0.00 - 0 .20%0.0036%0.00003%

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DISCUSSIONAlthough 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.

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