The German Shepherd is one of the most widely used breeds in a wide variety of scent-work roles. These include search and rescue, cadaver searching, narcotics detection, explosives detection, accelerant detection and mine detection dog, among others. They are suited for these lines of work because of their keen sense of smell and their ability to work regardless of distractions. At one time the German Shepherd was the breed chosen almost exclusively to be used as a guide dog for the visually impaired. When formal guide dog training began in Switzerland in the 1920s under the leadership of Dorothy Eustis, all of the dogs trained were German Shepherd females. An experiment in temperament testing of a group of Labrador Retrievers and German Shepherds showed that the Retrievers scored higher on average in emotional stability and ability to recover promptly from frightening situations, cooperative behavior and friendliness; while the German Shepherds were superior in aggression and defensive behavior. These results suggested that Labrador Retrievers were more suited to guide dog work while German Shepherds were more suited to police work. Currently, Labradors and Golden Retrievers are more widely used for this work, although there are still German Shepherds being trained. In 2013, about 15% of the dogs trained by Guide Dogs of America are German Shepherds, while the remainder are Labrador Retrievers and Golden Retrievers. The Guide Dogs for the Blind Association in the United Kingdom states that crosses between Golden Retrievers and Labrador Retrievers make the best guide dogs, although they also train some German Shepherds, as well as some other breeds. Guide Dogs for the Blind in the United States trains only Labrador Retrievers, Golden Retrievers and crosses between these breeds. Guide Dogs Queensland in Australia also trains only Labrador Retrievers and Golden Retrievers.