Impartial review, especially of work in less narrowly defined or inter-disciplinary fields, may be difficult to accomplish, and the significance (good or bad) of an idea may never be widely appreciated among its contemporaries. Peer review is generally considered necessary to academic quality and is used in most major scientific journals, but does by no means prevent publication of all invalid research. Traditionally, peer reviewers have been anonymous, but there is currently a significant amount of open peer review, where the comments are visible to readers, generally with the identities of the peer reviewers disclosed as well.