Hi
100% reduction in subjectivity is not possible. For people can misread, misinterpret & be biased.
However, degree of subjectivity can be brought down in anormal 90 degree appraisal system by
a) A review by second level manager
b) Normalization process by the final rating committee
Other methods are to adopt better systems ( may become administratively unwieldy) like 360 degree aprraisal system, which by virtue of multiple inputs from multiple sources can balance the extremes & reinforce what most people largely belive about an individuals performance.
Also , a better rewards & recognition system helps. After all, you try to assess the consistency in performance over a period of time. There may have been periods when there was an extraordinary spike or dip in performance. If you have schemes like Spot bonus etc, these spikes re rewarded & at the time of the final evaluation, these may be taken into account. The subjectivity of the normalization committee can be reduced to a large extent by keeping them informed abt these.
Regs