I saw this interesting note within a wikipedia link on 360 degree feedback.

'A study on the patterns of rater accuracy shows that how long the rater has known the person has the most effect on the accuracy of a 360-degree review. The study shows that subjects in the group “known for one to three years” are the most accurate, followed by “known for less than one year,” followed by “known for three to five years” and the least accurate being “known for more than five years.” The study concludes that the most accurate ratings come from knowing the person long enough to get past first impressions, but not so long as to begin to generalize favorably'

The original citation is shown on the wikipedia article.  We'll be looking at this ourselves and incorporating it in our own 360 degree appraisal recommendations at Bowland Solutions if it has a strong basis.

Brendan