An employee leaving out of the blue creates major hassles for employers. There are all the usual hiring and training costs, of course, but there is also the knock to team morale as those left behind scramble to cover for the departed employee. And there's the blow to your confidence as a manager too. How did you not see this coming?

An employee leaving is always disruptive, but it's much better if you can see that someone is eyeing the door. That way you can try to take measures to get them to stay, or failing that, make plans to lessen the impact of their departure. 

The key to doing that is to know well in advance who is thinking of quitting. A new survey of 34 million employees in 125 countries carried out by employee engagement platform Peakon insists it is possible. In fact, by looking for one telltale clue, managers can know nine months in advance who is considering quitting.

When engagement falls, it's time to worry.

The data set researchers analyzed for the study may have been huge, but their conclusions were clear as day. When it comes to figuring out who will quit, there's one indicator you need to watch for above all others -- employee engagement.

"Our study found that both employee engagement and employee loyalty scores are strong indicators of an upcoming employee departure. Nine months before quitting, an employee's overall engagement score begins to drop significantly," the report concludes.

The idea of employee engagement -- how invested in her work a given person is -- might sound vague, but according to the report, it can be measured by one simple question, known as the Employee Net Promoter Score: "How likely is it you would recommend [your company's name] as a place to work?"

"What makes this question work is that it encourages people to reflect on all aspects of their workplace experience at once--from company culture to work environment to career prospects. Also, a recommendation is a form of identity capital. Similar to when someone recommends a brand or product to a friend, an employee's willingness to recommend their company suggests they're aligned with their work on a deeper, more personal level," explains the report.

How to spot dipping engagement.

While it's a solid idea to send out an anonymous survey to your workforce asking this question, it's hard to put an individual worker on the spot with it. (Most nice people would lie and say, "Yeah sure, boss, of course I'd recommend this place.")  But there are signs you can look out for that are a good proxy for an individual's engagement with their work. 

According to research from two management professors written up on (and highlighted previously in my column), there are actually 13 behaviors that signal an employee is thinking of quitting. As I commented at the time, they all basically come down to phoning it in, also known as decreasing engagement with the work:

  1. Their work productivity has decreased more than usual.

  2. They have acted less like a team player than usual.

  3. They have been doing the minimum amount of work more frequently than usual.

  4. They have been less interested in pleasing their manager than usual.

  5. They have been less willing to commit to long-term timelines than usual.

  6. They have exhibited a negative change in attitude.

  7. They have exhibited less effort and work motivation than usual.

  8. They have exhibited less focus on job related matters than usual.

  9. They have expressed dissatisfaction with their current job more frequently than usual.

  10. They have expressed dissatisfaction with their supervisor more frequently than usual.

  11. They have left early from work more frequently than usual.

  12. They have lost enthusiasm for the mission of the organization.

  13. They have shown less interest in working with customers than usual.

These behaviors may all just be different flavors of lack of engagement, but by breaking down the phenomenon into parts, it gives managers very specific signs to look out for. Spot these changes in your employee, the Peakon report suggests, and unless you intervene, they'll be leaving your firm within the next nine months.

How to keep your employee from quitting.

If you do notice these early signs of a resignation in the works, how do you turn things around? The lengthy Peakon report goes into detail about just what drives declines in engagement (uninteresting work, feeling unable to talk about compensation, a bad manager) and what doesn't seem to matter as much (stressful but meaningful work, overall company culture).

If you're looking for ways to hold on to a valued but increasingly disengaged employee, it's well worth a read.