Dangerousness of dog bites, a validated evaluation
J. Dehasse*, A-C. Cornet
The aim of this project is to evaluate the dangerousness of dogs that have already bitten human beings. The usual way to do this is by means of an expertise such as a behavioural consultation. We combined the important (quantitative) variables on which this evaluation is based to build up an additive formula. Based on this formula we developed a scale of dangerousness.. The formula had been improved by multiple linear regressions. It is easy to use by people not qualified in behaviour.
are two steps in the development of a dangerousness scale and in its
scale was developed by insight on the basis of theoretical
modelling. The variables were selected and eliminated according to
what seemed to be heuristically and clinically operant, objective,
quantifiable, and easy to determine even for a person non qualified
selected variables are: mass of the dog and mass of the (bitten)
victim, categories of persons at risk (bitten victims),
offensive-proactive vs. defensive-reactive aggression, predictable
vs. unpredictable aggression, bite control, simple vs. multiple
bite(s) and held vs. non-held bite(s). At the beginning, each
variable received a value from 1 to 7, depending on the number of
items in each variable. This value was modified (weighted) after
statistical analysis of the variance of each variable.
Mass. The mass of the dog in relation to the mass of the victim is an
important variable to consider to evaluate the danger for the
victim. The variable is valued as follows: [4 x mass of the dog /
mass of the victim].
Victims. The same kind of bite will have different consequences for the victim
depending on whether the victim is a man or women, a child or an
elderly or handicapped person. . Epidemiological studies show that
children are in greater danger than adults (bites in the face,
etc.). The items are classified as follows:
Offensive (proactive) vs. defensive (reactive)
This variable describes the movement of the dog relative to that of
the victim. If the dog moves forward to attack the person who is at
some distance from it, the aggression is called offensive-proactive.
If the dog reacts aggressively to a person moving toward it, the
aggression is called defensive-reactive. The person can avoid the
bite easier if the attack is reactive; the attack is often more
severe if the dog is offensive-proactive than if it is
defensive-reactive. The respective values of these items are:
Predictable vs. unpredictable aggression. A
predictable attack is preceded by a well-organised and
understandable threat. A direct attack without any preceding threat
is unpredictable. The predictability has to be evaluated by the
victim. An attack is always unpredictable for children under 3 years
of age. It is evident that a predictable attack can be avoided more
easily than an unpredictable one. In the first case, it is probable
that the person can defend himself and thereby reduce the danger of
the bite. The respective values of these items are:
Control and intensity of the bite.
The less controlled the bite, the more intense the wounds and the
greater the danger for the victim. The respective values of these
Simple vs. multiple bites.
A dog that bites repetitively is more dangerous then a dog that
bites once. A dog that holds the bite is more dangerous then a dog
that pinches and lets go of the person immediately. The respective
values of these items are:
mathematical formulas have been established that link all these
variables. One formula is based on an addition, the other on the
multiplication of the selected variables. The multiplication model
may increase the risk of multiplication errors. A model based on an
addition is easier to apply for everybody, including
non-professionals. However, the best formula is the one that gives
the best correlation results with the expert considered as the
items [mass, victim, offensive/defensive, predictable/unpredictable,
control, simple/multiple] are x1, x2, x3,
x4, x5, x6, , respectively. All the
variables (x) are independent.
Multiplication model: y = x1 * x2 * x3 * x4 * (x5 + x6)
model: y = x1 + x2 + x3 + x4 +
x5 + x6. The addition formula is based on a
linear multiple regression model. The bi parameters are
estimated by the least square
method, a method assuming that the best-fit curve is the one
that has the minimal sum of the deviations squared (least square
error) from a given set of data (Efunda, 2003). Each variable
is analysed by a ‘t’ of Student test to determine if the
variable contributes to the explanation of ‘y’. All of the
variables should be statistically significant with an accepted
probability of 95%.
‘F’ of Fisher test is applied on the regression mean square: F = CMmodel / CMerror .
Each variable then receives a calculated weight (bi) coefficient, and a constant (b0) may be added: y = b0 + b1x1 + b2x2 + b3x3 + b4x4 + b5x5 + b6x6.
dogs were included if they had bitten people. Age or sex was no
criteria for selection.
behaviourist veterinary behaviourists from 3 different European
countries participated in the study. Where possible, the
veterinarians, or a technician present, evaluated the dog with the
dangerousness formula at the beginning of the behavioural
consultation. At the end of his/her behavioural consultation, the
veterinarian gave a subjective value from 0 to 10 to the
dangerousness of the dog examined; the value 0 means “no
dangerousness”, the value 10 “danger may be lethal”. Even
though the evaluation done during this consultation is subjective
and cannot be considered a golden standard, it is used as the
reference value to which the formula will be compared and
dogs were followed up for 3 months and incidents of biting were
total number of dogs included in this study was 86.
victims in the sample population were mostly female and adults.
attack was more often offensive-proactive (56 dogs, 65,1%) than
defensive-reactive (30 dogs, 34,9%).
attack was unpredictable in half of the cases.
bite level was generally controlled, leading to superficial wounds.
were generally simple and not held, leading to not too severe
of the dogs were evaluated to be of small to medium danger. This may
be a factor to help treating these animals.
dogs were euthanized (4,6%). 58 dogs (67,4%) received medication, 15
dogs (17,4%) did not receive any medication, in 11 (15,1%) cases it
was not specified. 73 dogs (84,9%) received a behavioural therapy,
in 11 (15,1) cases this was not specified. 18 dogs (20,9%) had
bitten again during the 3 months following evaluation and treatment.
breed of the dog is not taken into account in the variables. This
variable was rejected, as
not enough epidemiological validated studies exist that show the
influence of the breed on the degree of dangerousness of the dog.
other items, such as muscularity, type, diagnosis or context of
aggression, were not taken into consideration either, because
non-professionals might not be familiar with these items.
Additionally, they are not easy to objectify or standardize and they
may also not be independent of the chosen variables.
formula was analysed on the basis of a first sample of 44 cases of
dogs that have bitten humans examined by Joël Dehasse (2001). The
number of liberty degrees was (44 – 6 variables – 1 constant) =
37. This is enough to validate a multiple linear regression. The
core study was done on 86 cases. This number is quite small and the
statistician said that, to get the best results, one should use 200
five veterinarians participated in this study, the sample was not
distributed equally among them, two of the veterinarians evaluated
more than 75% of the cases.
dog was examined once by a veterinarian. Even if the variables are
quite easy to objectify, there could be differences of evaluation of
the same dog dangerousness by different experts. The analysis of the
objectivity of the
test has not been done.
this test have a predictive value? In order to find this out, the clinical case files
were re-examined to see if the dogs had bitten in the 3 months
following the clinical evaluation. Only the factor x6
(simple vs. multiple bite) showed a significant predictive value.
U Mann Whitney test between the dangerousness as evaluated by the
scale (formula) and the recurrence of biting is not significant (U =
329,5, p= 0,362). The formula is not predictive of recurrence of
biting. Only the x6 variable may be predictive.
this formula does not require any knowledge in ethology or in
behavioural medicine, non-experts (in veterinary behaviour medicine,
in animal behaviour therapy or in animal ethology) can use it as a
first criterion to determine whether a dog should be supervised,
euthanized or referred to an expert who will then decide on a
diagnosis and a treatment. Also veterinary surgeons in general
practice may use it to determine if the dog should best be referred
to a specialist or not.
formula may have a clinical prospective value if extrapolated from
one person bitten to another belonging to another victim category.
If a man has been bitten and the formula gives a value of 5, the
same bite would have produced a value of 9 if applied to his
formula, or at least the variables included in the formula, has a
pedagogic importance. In the case of intense emotion, which is the
case if somebody has been bitten, it may be required to rely on
logical elements of dangerousness, such as the ones analysed in this
It is possible and realistic to carry out a simple evaluation of the dangerousness of (a bite of a) dog without any specific knowledge of ethology or behavioural medicine. This evaluation could be handy for any veterinary surgeons (not specialised in veterinary behavioural medicine) anxious to get a first idea of the level of dangerousness of a dog biting within a specific environment.
Dr Joël Dehasse - Behaviorist veterinarian - www.joeldehasse.com - 2008-07-17