The student is quoting from page 15 of a working paper written by Andrew Cook, Martin Gaynor, Melvin Stephens Jr., and Lowell Taylor and published in 2012. This is the first reference to the source in the paper.

While the authors admitted that it was difficult to generalize “causal inferences” based on the results of their studies, they explained that “those hospitals that are most effective in ensuring patient safety generally find it optimal to employ more nurses per patient” (Cook, Gaynor, Stephens, & Taylor, 2012, p. 15).

While the authors (2012) admitted that it was difficult to generalize “causal inferences” based on the results of their studies, they explained that “those hospitals that are most effective in ensuring patient safety generally find it optimal to employ more nurses per patient” (Cook, Gaynor, Stephens, & Taylor, p. 15).

The date belongs in the parentheses with the authors’ names, not after the word authors.