Recently, a novel reversible data hiding method based on pixel value ordering, also called PVO, has been widespread concerned by the researchers in the field of data hiding, because the incorporation of PVO-based reversible data hiding reduces pixels modification, and thus it can contribute in the high fidelity of image quality. To date, several improvements of the PVO method originated form Li et al. have been proposed. In order to increase the embedding capacity and preserve good image quality, most of authors make the proper use of the image characteristics, such as pixel correlations, block textures and region complexity, etc. In this paper, various PVO-based reversible data hiding schemes are studied. The analysis and comparisons among those methods are discussed such that the researchers who are interested in the field can catch the essence of PVO methods.