Michael Nielsen says it's "very, very difficult for even the best scientists to accurately assess the value of scientific discoveries," which partly explains why some of the most influential revelations — like Einstein's theory of gravity — "were initially underappreciated." Despite their participation in a discipline so deeply vested in metrics and statistical significance, scientists have not yet determined the best way to judge the value of research, Nielsen says. Still, while "it may be near-impossible to accurately evaluate scientific work, as a practical matter we are forced to make such evaluations," he says. "Every time a committee decides to award or decline a grant, or to hire or not hire a scientist, they are making a judgment about the relative worth of different scientific work." In an essay on his blog, Nielsen suggests that "heavy reliance on a small number of metrics," such as h-index values and citation counts, "is bad for science."