Facebook conducted a study in January 2012 to see how the placement of positive or negative words in the news feeds of users affected their status updates.
The results of the study, conducted on 700,000 users, were published in an article in the journal 'Proceedings of the National Academy of Sciences'.
This stirred a global debate on privacy and protection of user data.
"This was an experiment done for one week, this was communicated terribly and for that communication, we have apologised. This is part of the ongoing research that companies do to test different products," Sandberg told reporters here.
She added that Facebook, which is the world's largest social network with over 1.2 billion users, takes privacy and security very seriously. In India, Facebook has over 100 million users.
Previously, Facebook data scientist Adam Kramer, in a post, had also said the goal of Facebook's research is to learn how to provide a better service.
A UK regulator has begun an inquiry into the experiment to determine if the company broke data protection laws applicable in that country.
"We work very closely with the regulators all over the world ... we are fully compliant (with regulations) (respect for data privacy) is the hallmark of our service, it is the underpinning of our service," Sandberg said.