Yep, the personality questionnaires are all to do with correlation. I think over the whole process you do about 4 or 5, normally all asking similar things, just worded differently. If you answer one question with one answer, and then another similar question with a completely different answer, then this will flag up as an inconsistency. One or two inconsistencies are fine, but a lot will flag up something to HR.
In fact, I apparently had some inconsistencies, and they actually asked me straight out in the stage 3 interview about it, so obviously it wasn't bad enough to fail me there and then, but still serious enough to question me about it. I explained myself (it was something about "do I look to the future" or something) and I found it much easier talking myself than picking a multi choice answer.
So answer honestly, yes, and you should be fine as all your answers will usually match....The worst you can do is think what they want, because it really doesn't work like that. Me and this other girl put completely opposite answers to one another, and we both got through. I think there's a great emphasis on consistency, rather than actual answer.
(Though obviously, if you answer things like "no I never exercise", "I like sitting on my bum all day every day eating pies", "I don't like working" and "I hate talking to people", then that ain't going to help. But in all honestly, I guess those personalities don't generally try to join NATS as ATCOs, or do they?!)