A New York Timesarticle published on April 24, 2007, reported the research of Dr. Giorgio Vallortigara, a neuroscientist at the University of Trieste, Italy, and his colleagues. In this study, the researchers investigated whether a dog's tail wags in a preferred direction in response to positive as opposed to negative stimuli. The researchers answered this question by recruiting 30 dogs that were family pets. Filming the dog's tail from above, they allowed each dog to view (through a slat in its cage) its owner, an unfamiliar human, a cat (positive stimuli), and an unfamiliar, dominant dog (a negative stimulus). Would it be appropriate for the researchers to use a parametric hypothesis test

A dog's tail will wag differently in response to positive stimuli and to negative stimuli.

Explanation:

Dogs wag their tail for various reasons. Most times it is not just done when the are happy but also when they aren't. Dogs wag their tail to convey various messages, but what is very obvious is how it's wagged when they are happy seeing their owners. When a dog is relaxed, the tail is wagged gently, and in most cases a reaction to objects that come in contact with them.

A dog's tail is not wagged only to either positive or negative stimuli but rather to both of them.

answer; i believe that the correct answer is (decreased)

you should think about the answers you give and expect the same form your questions.