Understanding Society User Support

Hello,

I'm currently studying Understanding Society Waves 1-3 in relation to travel behaviour and social trends, but need clarification on an issue. In Wave 1 for example in the a_worktrav variable 50% of responses were (-9) inapplicable. What does this actually mean?

Similarly, I have seen in another project a list of travel modes which includes 'working from home' amongst the other responses from _worktrav e.g. bus, car, walk etc. but cannot find this, at least not in Wave 1. Does this mean the work from home option in included in the inapplicable one?

Cheers,
Rob