Estimated hash rate is NOT an accurate report on a given miners actual hash rate, it is heavily affected by luck/variance and does not take doa/stale shares into account.
If your reported rate is higher then actual rate you are currently lucky in finding shares.
It is calculated as follows:
estimated_hash_rate = (current_payout / block_value) * pool_rate
current_payout = Miner current expected payout.
block_value = The total reward for the block this node is working on.
pool_rate = P2Pools reported /rate.
(results formated to GH/s)