0.25 stars!!!! It's a shame that this thing is sold as a text book! Error-ridden and and not very comprehensiveness. The number of errors, especially when it comes to mathematical equations and graphs is ridiculous and whilst simple concepts are rephrased about three times for some strange reason, may be the authors thinks the reader doesn't get it the first time and is too stupid to re-read it, the more complicated stuff, mostly involving statistic are so in comprehensive that the reader needs the internet to understand what is going on and discover that the whole thing wasn't complicated at all!