Preferred are single spaced block quotes. In either case, indent the left margin five spaces, and type the right margin as you normally would. How often these social scientists say blah blah blah. Entire dissertations sometimes have the same theme. This goes for any style book, really.
Ellipses give some writers fits.
When I was a small-town newspaper editor, we had a woman in a neighboring town writing one of those gossip columns. We paid her by the column inch, so on a good week I could cut a buck or two off her paycheck by deleting all her extra periods. But I digress. To show that you are omitting words that appeared in another source or in the text of an interview, in the middle of a sentence, you space three dots like this . . . At the end of a sentence, you use four dots, the first right after the last word, as a period, like this. . . .