Why are dashes rather than parentheses or commas used in this sentence

-Parentheses are used to set off a participle word or words which can be omitted, but does not affect the whole thought of the sentence. In addition, parentheses could also be used to add a specific detail about the word beside it.

-Dashes are used to set additional information off. Dashes are commonly used if the words it enclosed already has a comma or commas in it, just to avoid confusion.

answer; i believe that the correct answer is (scientific data);