The influence of the experimenter’s expectancy in the results of the assessment of appeasing pheromones in stress of police dogs during training (abstract)

© Dr Joël Dehasse, S Schroll
3 avenue du Cosmonaute, 1150 Brussels, Belgium-

Abstract proposed and accepted at the 5th International Veterinary Behavioural Meeting, Minneapolis , USA , July 14, 2005 (Full text)


The purpose of this preliminary study was to reduce the stress of police dogs during a 4 week training course with the use of dog appeasing pheromones (DAP), the DAP being released from a collar the dogs were wearing all the time. 
After a family life and basic education for one and a half year, police dogs are separated from their families and gathered at a dog training centre to undergo an intensive training course of 15 weeks at the end of which they pass tests deciding on their future career. Previous training courses have shown that the dogs are stressed as witnessed by symptoms such as barking at night, insomnia, weight loss, diarrhoea, salivation, loss of concentration, exhaustion, poor performance… The experience is also very stressful for owners (police people) whose dogs will be judged apt or inapt to continue as police dogs. The experience was stressful enough to be mandated by the Ministry of Defence and the Police Corp.


Materials and method

Double blind placebo-controlled 4 week study; of nine police dogs undertaking a 4 weeks training course, five dogs were wearing DAP collars and 4 dogs were wearing placebo collars. As indicators of stress levels, weight, (salivary) cortisol and different physiological and psychological parameters were evaluated at the beginning, during and at the end of the trial.

The Ministry, Police officials and dog owners were informed of the experimenters expectations of reducing stress and were taught about stress indicators. 



Nearly significant results were found for the weight loss (p=0,069) and significant results for cortisol samples (p=0,016), the placebo dogs losing weight and showing cortisol elevation (during the second week) but not the DAP dogs. All dogs slept peacefully and none barked at night, contrary to the best expectations. 



The reduction of barking and insomnia at night was expected in DAP dogs, not at all in the placebo dogs. The tranquillity of placebo dogs at night is not easily explained. It makes us think of the Hawthorne , Pygmalion or Experimenter effects (Draper). Talking about experimenters’ expectations to the police officials and dog owners may have influenced the outcome of the training results and the well being of the dogs. Another possible effect could be related to a distant healing effect as significantly evidenced by Sicher and Targ on human patients with terminal AIDS: having a focused intention to modify a situation may already have significant effects on the results.

In conclusion, the beliefs of the experimenter may affect the results of experimentations. By extrapolation in a clinical therapeutic approach, we might hypothesize that the beliefs of the counsellor might affect the results of his/her treatments. 



Data analyses were made with the Mann-Whitney test, the Wilcoxon and the Fisher-Yates test, using  SPSS program.

  • Draper SW. 2005 (Feb 5). The Hawthorne effect and other expectancy effects: a note. [WWW document] URL (visited 2005 March 23)

  • Schroll S, Dehasse J. 2005. The use of a DAP collar to reduce stress during training of police dogs, a preliminary study. Proceedings of the 5th International Veterinary Behavioural Meeting, Minneapolis , USA , July 14, pp.

  • Sicher F, Targ E, Moore D, Smith H. 1998. A Randomized Double-Blind Study of the Effect of Distant Healing in a Population With Advanced AIDS: report of a small
    scale study. Western Journal of Medicine, 168 (6): 356-363.


  • Some info on Targ (Russel) and Distance Healing (...)

Dr Joël Dehasse - Behaviorist veterinarian - 11/12/2005