We have a social networking site and are trying to measure engagement - can any body advise me how to get an estimate of daily session time per UV. We have tried variuous arithetic ways of doing this using UVs, average session time and the number of days in a period 30, 7, 1 day depending on the whether its monthly Uvs etc. However, the daily session time vary widely. Any clues anybody?

Regards

Jim