How useful is a survey like this? The survey does not define burnout to employees, leaving them to guess at the definition. Can employees reliably self-diagnose burnout and differentiate it from similar conditions - i.e. actual depression? Can they also reliably indicate the cause for the burnout, especially if the symptoms can overlap with the cause? Let's say you have burnout because of work overload, but you normally don't mind doing tons of work, just hate your boss. When the feelings of exhaustion/anger come up, will you point them at the work load or at your boss?
Perhaps you could relabel it as a survey on workplace discontent, but even then, I don't think it's really well made. The problem with statistical data like this is that we can see the primary source and temper our enthusiasm for the accuracy of the survey, down the broken telephone line, it will be taken as gospel(see the wage gap/sexual harassment statistics as examples).