From SEO Moz:
Their feedback is aggregated and averaged into the percentage scores below. For each, we’ve calculated the degree to which the experts felt this factor was important for achieving high rankings as well as the degree of variance in opinion, estimated using the standard deviation of the contributors’ answers. Thus, factors that are high in importance and low in contention are those where experts agree the most that the factor is critical to rankings.
These guys know their stuff and this info is worth knowing.