All good points, thanks. 14. Yes, that was a mistake, sorry. 32. Agreed, edited to avoid confusing people. 34. Agreed and added. 46. Yeah, one isn't always discarded. For example, humans are pretty good at compartmentalising. 47. Maybe not a concept, (I'm not one to quibble of definitions - http://lesswrong.com/lw/np/disputing_definitions/) but I feel as though it can be useful. Beyond the formal use, it can be helpful to think about how much variance is explained in a model by any particular attempt. For instance, say someone claims that women are bad at giving directions. Even if on average this is true, gender might only account for a small amount of differences in direction-giving abilities. In this example, you'd want to see some data, but at least it can be instructive to how one might conceptually picture the claim someone is making.