Justified Bite Ratio

by Bill Lewis II

I do not believe the standard formulas for establishing bite ratios today are an accepted standard by which to judge or prejudge the effectiveness or performance level of a department’s K9 program.  If you are required to keep bite ratios or contemplating doing so, or looking for a more efficient way to justify the number of bites based on a ratio, I’ve provided some opinions herein and a recommendation that you may consider to assist in better evaluating your K9 program with respect to bite ratios.

Bite Ratio Formula

Traditional bite ratios are not a true measure of a K9 program’s overall effectiveness nor the means alone to evaluate an individual handler’s performance.  Bite ratios do not determine how levels of force are measured when simply converted to a simple mathematical equation nor do they “act as a barometer for misconduct and measured police violence” as indicated in two studies often referred together as “the Florida study” authored by Charles Mesloh titled “An Examination of Police Canine Use of Force in the State of Florida” dated Summer 2003 and “Barks or Bites?  The Impact of Training on Police Canine Force Outcomes” published in September 2006.

Effectiveness and performance should be measured by a review of each and every individual deployment and the accessibility – or not – of the persons that are apprehended by a bite or a surrender without incident within the area of deployment.

The industry standards for establishing bite ratios are not consistent.  Based on informal surveys I’ve conducted of students (handlers and K9 supervisors) across the country who attend my canine liability classes, most agencies do not keep bite ratios nor are required to do so.  Some departments calculate their ratio based only on bites and the number of suspects located (bitten or not).  Other departments calculate the ratio on bites and the number of total deployments where any bite opportunity exists – whether to a suspect, officer/deputy on scene, or a bystander.  The latter ratio is most consistent in terms of litigation, lawsuits and claims that I have experienced where people sustain a bite because each and every deployment has an opportunity for a bite to occur – accidental, negligent or justifiable.

It is my recommendation that standard (“old school”) bite ratios not be kept***, and if a traditional standard bite ratio is required, the formula should be based on the number of bites and the number of overall deployments where a bite opportunity exists regardless of the presence or not of a suspect – but I have a better recommendation for keeping a ratio.

***Author’s Update:  I have recently reversed my opinion regarding standard bite ratios and the necessity of keeping them.  Although I’m still of the opinion these bite ratios do not measure the overall effectiveness of a K9 program, I believe they should be kept and shared to defend a program, particularly when an agency is wrongly accused of something like “their dogs bite everyone they find.”  (Hopefully, your dogs aren’t biting everyone.)  For example, the primary mission of most agencies using police dogs is to locate a suspect.  If your bite ratio is 100%, your dogs are biting everyone.  If your bite ratio is less than 100%, your dogs are not biting everyone.  If your bite ratio is less than 50%, the majority of your deployments are not resulting in bites.  We must defend our K9 programs nowadays by showing the number of suspects not bitten.  Here’s how to put a positive spin on bites with respect to an agency with a 14% bite ratio;  “86% of the deployments involving our K9 teams do not result in a bite to the suspect.”  (updated on May 25, 2021)

“The 20% Trigger”

Bite ratios were addressed in 1989 in Kerr v. City of West Palm Beach 875 F. 2d 1546 (11th Cir. 1989) that said “One indication of a misbehaving dog is a high ratio of bites to apprehensions. Less than 30% of apprehensions, on an average, should result in a bite. Thus, canine units with a bite ratio exceeding 20% should be reviewed.”

A high bite ratio might be an indication of a misbehaving or incompetent K9 handler.  However, a high bite ratio might also be an indication of a highly active K9 team working in a high crime area with more direct accessibility to suspects that meet the criteria for a justified deployment.  In the majority of bad bite incidents, the handler is 95% (or more) responsible for the actions that resulted in the negative result.  It is the behavior, actions and competency of the K9 handler that requires continual reviews and evaluations.

I’ve read that some police departments require supervisors automatically to review the performance of any canine unit with a bite-ratio of over twenty percent in order to ensure that misbehaving dogs receive prompt corrective training.  I have never seen nor have knowledge of a department that utilizes an established bite ratio formula to trigger a review of its K9 program.  And, a department that waits for “the 20% trigger” is doing a disservice to its program.

The percentages often recommended (20%) and considered by some to initiate a review of a K9 program are unsupported by any evidence or studies to prove these percentages are the benchmarks by which a review such be initiated.  There is no evidence to support a bite ratio of 20% should be the accepted standard to trigger a review of a K9 team or K9 program versus 25% nor is there evidence or studies that one number is more of an effective indicator than the other.  K9 programs and deployments involving bites should constantly be reviewed as a matter of practice regardless of a bite ratio.

One bad bite should trigger a review, not a ratio of 20% total bites that may or may not even include a bad bite.  However, a high ratio of bad bites within this overall ratio that have not been addressed would be viewed as a failure to properly supervise the program.  Your policy should require the K9 Supervisor to complete thorough post deployment reviews of all canine deployments to satisfy an ongoing review of your program as long as such reviews include any corrective actions, remedial training and disciplinary action that may be deemed necessary and appropriate.

If a police dog has a bite ratio of 35% and each bite was deemed to be justifiable, this ratio has no relationship nor evidence to identify a misbehaving dog (or handler) and the dog was obviously accomplishing its mission when deployed – to bite if the opportunity presents itself.

A department that constantly reviews its deployments (and bites) and responds appropriately does not require “the 20% trigger” to start a review of an individual or unit.  I recommend you eliminate and avoid any references to a percentage that may trigger a review if you have such and contain within your policy that the K9 program is constantly being reviewed, including, but not limited to, every incident involving a bite by a police dog.

Justified Bite Ratio

One of many problems with these standard bites ratios is the inability to determine whether a bite is justified or not based only a ratio.  Is a handler with five legitimate and justified bites in five deployments (100% bite ratio) the product of a poorly trained and supervised K9 unit compared to a handler with a dog that bites one but would not or could not bite five other suspects in six deployments (17% bite ratio)?  Both handlers were successful.  How would one compare effectiveness of a K9 program with a bite ratio of 18% that includes 8 bad bites to a program with a bite ratio of 23% and no bad bites?  It is statistically impossible to make such a comparison based on a ratio versus a review of each program and incidents involving bites.

I’ve been actively involved with the police K9 community for over 28 years in various capacities and, based on my experiences and interaction with attorneys, handlers and K9 supervisors across the country, I believe a more efficient means to evaluate the effectiveness of a K9 program with respect to its K9 deployments (and bites) and the performance of its handlers is a “justified bite ratio” that determines how many bites have occurred and have been investigated and deemed to be justified and within department policy.

An example of the justified bite ratio would be a department with 12 bites that have all been investigated and determined to be within department policy and they would report a 100% justified bite ratio.  The same numbers can apply to an individual handler.  A department (or handler) with 11 bites deemed within policy and 1 bad bite would report a 91.6% justified bite ratio. These percentages are the best factor and most transparent means to evaluate a K9 program.

It is my recommendation that your K9 program consider adopting a “justified bite ratio” as described to assist your ongoing program evaluation, and/or in lieu of or in conjunction with the standard bite ratio previously recommended.  By adopting a justified bite ratio, you can also establish annual 100% goals for each handler and the unit.

Bill Lewis II © August 2017