What does survey completion tell you about your team

I've just read on another well-known HR website that we shouldn't get too hung up on response rates for a staff engagement survey - it's OK if half the staff fill it in, we needn't worry about the rest.

Well, that can't be right. If half the staff are responding, which half would that be?  The more engaged half, of course.  And which half needs to change?

The trick is to design a staff engagement process which the less-engaged staff actually want to take part in. In fact that is surely the real measure of an engagement exercise, that it reaches the parts of the team that have always been hard to reach.

A great deal of effort goes into making survey design efficient, so that the burden on employees is no greater than it needs to be. One reason for doing this is to increase the completion rate, on the assumption that people are more likely to do something if you make it easy.