How to cite multiple papers published in different years by the same authors in APA style? http://www.easybib.com/guides/citation-guides/apa-format/how-to-cite-a-parenthetical-citations-apa/

In APA style, we have to use ampersand(&amp;) instead of 'and' when we cite multiple authors in the parenthesis.

Ex) This is the sentence (Smith &amp; Williams, 1989).

When I cite two papers by the same author, should I use comma, or 'and' or ampersand?

(1) This is the sentence (Smith, 1989 &amp; 1991).
(2) This is the sentence (Smith, 1989 and 1991).
(3) This is the sentence (Smith, 1989, 1991).

What if there are three or more papers?

(1) This is the sentence (Smith, 1989, 1991, &amp; 1993).
(2) This is the sentence (Smith, 1989, 1991, and 1993).
(3) This is the sentence (Smith, 1989, 1991, 1993).
These are the examples given in the sixth edition of the APA manual. They are separated only by a comma.

Training materials are available (Department of Veterans Affairs, 2001, 2003)
Past research (Gogel, 1990, 2006, in press)