top of page

Factors Influencing Reliability

Writer's picture: Stephen BissStephen Biss

Updated: Aug 9, 2022

What is "reliability" in the context of a "quantitative analysis"?


What does "reliability" mean in measurement science?


We have a definition of INSTRUMENTAL "reliability" from Hodgson (Hodgson, Brian T., "The Validity of Evidential Breath testing", Can. Soc. Forensic Sci. J. Vol. 41 No 2 (2008) pp. 83-96) in the paper cited by the SCC in R. v. St‑Onge Lamoureux, 2012 SCC 57 (CanLII), [2012] 3 SCR 187, <https://canlii.ca/t/ftl1g>, but:


  1. Are there additional components to instrumental "reliability" other than drift in accuracy and precision over time?

  2. Are there additional components to "reliability" of a quantitative analysis measurement result other than instrumental reliability?

  3. Are there, for example, human factors, that influence reliability of a measurement result, notwithstanding automation?

  4. Is there, for example, a traceability factor, that influences reliability of a measurement result, notwithstanding automation?



Purpose of this sample cross-examination:


To obtain admissions from a CFS scientist respecting the factors that influence reliability in a laboratory


To suggest that there are multiple components to "reliability"


To lay the groundwork for an argument that reliability means a lot more than a formula of two tests 15 minutes apart with 02 agreement and control tests between 90 and 110


To define scientific "reliability" using ISO 17025



Title page to ISO 17025
Paragraph 5.1.1 from ISO 17025 many factors determine correctness and reliability
Paragraph 5.1.1 in ISO 17025 2005

Q. Can I just ask you please to move ahead please to page 10 under paragraph 5? Certainly from – in a laboratory context, the description there at 5.1.1 indicates that there are many factors that determine the correctness and reliability of the tests and or calibrations performed by a laboratory. They include human factors. Is that consistent


with your experience? A. Yes.

Q. Accommodation and environmental conditions. I guess that can include temperature. A. Yes. So, human can – human condition – human factors would be such as an individual’s accidentally switching the vials, or the order or the vials that the analysis is done in. Q. Test and calibration methods and method validation. A. Yes. Q. Equipment, again, that’s consistent with your experience and the work that you do in a laboratory. A. Certainly is, yes. Q. Measurement traceability. A. Yes. Q. Right? And – and again, what’s measurement traceability? Can you help us with that please? A. So, in that case, the analysis that’s performed and the accuracy of that analysis is related to a specific parameter. So, you have an alcohol standard solution that is certified by the manufacturer to have this concentration in it, and that is something that you can then use to relate to the concentration of the unknown in a particular sample. So, you produce a calibration curve that we described earlier, right, well, varying – increasing concentration and those standards are certified to contain a certain amount of alcohol that can then produce a response, in relation to the concentration and then you compare your unknown to that to get the actual concentration. Q. But measurement traceability, the traceability is between the measuring device and the


standards, the reference standards that were used in the calibration of that device, right? A. That's correct. So, we have standards that are certified. We also have pipets that are calibrated and checked on a very regular basis to make sure that they haven’t drifted at all.


[Note to defence practitioners. Where does the "traceability" component of reliability come from? The traceability of the measurement result to alcohol standards, acknowledged by the CFS expert here, relates to the alcohol standards USED AT THE FACTORY TO CALIBRATE THE INSTRUMENT, NOT to the alcohol standard used at TIME OF INSTRUMENT USE with your client.}

37 views0 comments

Recent Posts

See All

If you are a member of the public, please don't attempt to use what you see or read at this site in Court. It is not evidence. The author is not a scientist. The author has a great deal of experience in cross-examining scientists about these issues, but the author is not a scientist. Hire a criminal lawyer in private practice in Ontario. Your lawyer can retain an expert. The author is a retired lawyer, not a lawyer in private practice. Read the statement of the purpose of this web site below.

© 2025 Allbiss Lawdata Ltd.

This site has been built by Allbiss Lawdata Ltd. All rights reserved. This is not a government web site.

For more information respecting this database or to report misuse contact: Allbiss Lawdata Ltd., Mississauga, Ontario, Canada, 905-273-3322. The author and the participants make no representation or warranty  whatsoever as to the authenticity and reliability of the information contained herein.  WARNING: All information contained herein is provided  for the purpose of discussion and peer review only and should not be construed as formal legal advice. The authors disclaim any and all liability resulting from reliance upon such information. You are strongly encouraged to seek professional legal advice before relying upon any of the information contained herein. Legal advice should be sought directly from a properly retained lawyer or attorney. 

WARNING: Please do not attempt to use any text, image, or video that you see on this site in Court. These comments, images, and videos are NOT EVIDENCE. The Courts will need to hear evidence from a properly qualified expert. The author is not a scientist. The author is not an expert. These pages exist to promote discussion among defence lawyers.

Intoxilyzer®  is a registered trademark of CMI, Inc. The Intoxilyzer® 5000C is an "approved instrument" in Canada.

Breathalyzer® is a registered trademark of Draeger Safety, Inc., Breathalyzer Division. The owner of the trademark is Robert F. Borkenstein and Draeger Safety, Inc. has leased the exclusive rights of use from him. The Breathalyzer® 900 and Breathalyzer® 900A were "approved instruments" in Canada.

Alcotest® is a registered trademark of Draeger Safety, Inc. The Alcotest® 7410 GLC and 6810 are each an "approved screening device" in Canada.

Datamaster®  is a registered trademark of National Patent Analytical Systems, Inc.  The BAC Datamaster® C  is an "approved instrument" in Canada.

bottom of page