Other behaviourists believe that the use of verbal corrections, head collars, correction collars, or electric collars are necessary or useful when treating particular dogs or particular behavioural problems. The general philosophy in use is to avoid methods that could cause confusion, fear, pain and anything other than mild stressors. Dog trainers who use these techniques may or may not be utilising a behavioural approach and may or may not have an understanding of the science behind behaviour modification. Dog behaviourists who lack professional credentials are generally dog trainers who have developed their expertise for working with problem dogs over many years of hands-on experience. They may or may not have studied behaviour formally in college or any dog training school.