As part of the one-week experiment, which recently came to light, Facebook manipulated users' news feeds to test their emotional responses to more positive or negative posts.
News of the study incited uproar on social media last week. On Wednesday, Sandberg became the highest-ranking Facebook official to respond to the controversy.
"This was part of ongoing research companies do to test different products, and that was what it was; it was poorly communicated," Sandberg told the Wall Street Journal. "And for that communication we apologize. We never meant to upset you."
The study's authors found that Facebook users were more likely to produce negative content when they were shown negative content and vice versa.
Adam Kramer, one of the study's authors, apologized in a Facebook post.
"I can understand why some people have concerns about it, and my coauthors and I are very sorry for the way the paper described the research and any anxiety it caused. In hindsight, the research benefits of the paper may not have justified all of this anxiety," he wrote.