Stephen Few has an excellent overview of why pie charts should be avoided: http://www.perceptualedge.com/articles/visual_business_intelligence/save_the_pies_for

Stephen Few has an excellent overview of why pie charts should be avoided: http://www.perceptualedge.com/articles/visual_business_intelligence/save_the_pies_for_dessert.pdf http://www.perceptualedge.com/articles/visual_business_intel... Neither pies nor mosaic charts should be used if you need exact readings of the data --- though mosaic plots do have the advantage of being rectangular, making segments much easier to label with values than the segments of pie charts.