A scientific review paper I authored was recently published in the Journal of Veterinary Behavior - Clinical Applications and Research. You can see the abstract and short presentation here.
This review summarizes 17 peer-reviewed studies that compared training methods. Mainly, reward-based methods (i.e., based on positive reinforcement) were compared to aversive training metohds (i.e., based on positive punishment and negative reinforcement).
While there were several methodological concerns in the reviewed studies, the results are still clear:
- not one of the studies showed that aversive training methods are more effective than reward-based methods. in fact, at least according to three of the studies, the opposite is true! reward-based methods can be more effective than aversive training methods.
- aversive training methods are accompanied by unwanted side-effects that can be seen in dogs' body language (lower postures, lower tail carriage, etc.) and stress hormone levels.
The results of this review suggest that owners, trainers, behaviorists, and veterinarians should avoid using aversive training methods in dog training. Recommendation to train behaviors or modify behavior problems should be based on reward-based, humane methods.
If you are interested in learning more about the unwanted side-effects of aversion I would highly recommend Murray Sidman's excellent book - Coercion and its Fallout. While this book discusses the effects of aversion on humans, it is still a must-read for everyone teaching or training living organisms.
While this book is out of print for quite some time, I encourage you to make an effort to buy a used copy. I will be very surprised if you do not find this book useful for your practice.