There has been a ton of research over the years on why employee engagement matters.

For example, a report earlier this year from Microsoft’s WorkLab —which “delves into the latest science and the most innovative thinking … about how and where and why people work”—found that “high employee engagement correlates with stronger financial performance.”

There are many reasons for this bottom-line impact. We’ve known about them for years. A 2013 Harvard Business Review article identifies several of them: because companies with highly engaged employees report higher levels of productivity, lower levels of absenteeism and turnover, and fewer safety incidents and quality problems.

Setting aside the concern that correlation doesn’t prove causation, let’s accept the fact that in this case these and other studies over a long period of time have certainly provided strong circumstantial evidence. But they also raise an important question: What does “engagement” mean?

My home-grown formula for determining engagement is pretty straight-forward: Those who enjoy their work will be engaged. Those who see their jobs simply as pay checks, necessary to pay the bills, will be less engaged. And those who consider their jobs drudgery will drag their teams down, chalk up more absences, job-hop more frequently, produce less, and make more mistakes than those who are happy.

The BCG Henderson Institute, Boston Consulting Group’s internal think tank, recently conducted a wide-ranging survey that adds some much-needed richness to this discussion.