I realize there is a somewhat similar question posted, but my question is different in that I found a pretty big mistake in my thesis. It's such a big problem, it changes my results. I almost wish I hadn't noticed, and been so careful to go back and check every thing, because I really don't know what to do about it except fix the errors/interpretation errors and discussion (today). I defend very soon (in days). It's possible that my committee won't notice it, but I feel like the guilt might drive me insane. I'm worried that my chair noticed it in the past, but they didn't correct me because they feel I'm incompetent (which I feel in ways I am when it comes to stats). Should I re-write it and let my chair know and ask what to do? I need to defend soon in any case. I wonder if I could just present as though I'd already corrected it and e-mail the revised manuscript beforehand. I'm just not sure how they would perceive someone who overlooked such a obvious mistake. Any advice would be appreciated.