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George, you sidestepped a direct answer to both questions, professing ignorance. That surprises me. I have obviously overestimated your knowledge of the polygraph, their operating systems, and their scoring algorithms.
The operating systems of all North American made digital polygraphs (and likely all digital polygraphs worldwide) are explicitly designed to store the raw physiological and audio/video data in a protected file that cannot be tampered with once each chart is completed. It is necessary for those data to be inviolate so the test can be reviewed for quality control or evidentiary use. An examiner cannot alter the original data post hoc. Even when the exam is copied for review, the reviewer receives a true copy of the original data. The audio/video is time-locked to the charts, so that the reviewer can easily verify that the questions had not been manipulated, such as by asking a different question than the one marked on the chart. Thus, the correct answer to my first question is no, an examiner cannot change a DI chart to an NDI chart (or vice versa) by manipulating the results after the test is over. My wording may have been imprecise; instead of “results” I should have said “raw data.”
What examiners and reviewers can change is the size and position of the physiological channels (respiration, electrodermal activity, cardio, plethysmograph, and movement) for optimal viewing on the screen for analysis. In the old days with paper charts from analog polygraphs, when the test was over, the charts had to be interpreted as is. If the sensitivity of the electrodermal channel were too low so that the reactions could not be seen; or if the sensitivity were too high so that the pen hit the pen stop or went off the top of the chart, it was impossible to know how big the reactions were. Sometimes the pens snagged, which prevented both channels from recording properly. Occasionally the ink would stop flowing or flow too rapidly from the pen, and the tracings could smear and become illegible. Not infrequently two channels overlapped with each other (for example, if the electrodermal pen moved into the respiratory tracings) until the pens could be manually re-centered. In every case, when the chart was over, you were stuck with what you had.
With digital technology, these problems are a thing of the past. The examiner or reviewer can re-adjust the amplitude of each channel, if needed. Now before you say, “Aha! There’s the smoking gun,” you must understand that the examiner cannot enlarge the response to any one question in isolation; the enlargement (or reduction) is applied equally for all questions for that channel on that chart. For example, if the beat-by-beat amplitude of the cardio tracing was so high during the exam that it ran into the other tracings, the reviewer could reduce the amplitude after the test, but it would reduce the cardio on all questions equally. The examiner can also reposition a tracing upward or downward on the computer monitor to avoid overlapping channels. Optimizing the channels is usually done in an effort to avoid an inconclusive result, on cases going to court, or when the charts are being analyzed for countermeasures.
The computer scoring algorithm normally agrees with the examiner’s scoring. When there is a difference, it usually is when the examiner considers the exam inconclusive but the algorithm recommends a decision. Only rarely does the algorithm come to the opposite conclusion than the examiner’s decision. When that does happen, the examiner’s evaluation is generally accepted as the “official” result; the algorithm is considered a supplement, not a replacement for the human evaluator. Keep in mind that there are perhaps five different scoring algorithms commonly available in North America, and they don’t always agree among themselves. Each analyses the data differently.
There is nothing nefarious or unethical about optimizing the charts for analysis. This is a common practice within many disciplines where digital images are analyzed by trained professionals, such as dental x-rays, mammograms, and microscopy. The reviewer can zoom in or out, enhance the contrast, etc. in order to arrive at a more detailed analysis.
My optimization of the chart for analysis had absolutely no bearing on whether the algorithm agreed or disagreed with my conclusion. To suggest otherwise (and you put quotation marks around optimize as if to imply it was unethical) betrays a surprising ignorance of polygraph procedures. Your implication about my integrity calls to mind a Chinese proverb: “One’s suspicion of others if often based on one’s knowledge of oneself.”
Peace.
Gordon
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Computer-based polygraph: can the chart be altered by the examiner? (Read 7785 times)
