Remove duplicate records with timestamps
So doing a join on the elements that constitute a duplicate and the last where criteria shows which to delete.

delete t1
from table t1, table t2
where t1.user_id = t2.user_id and t1.stat1=t2.stat1
     and t1.stat2=t2.stat2  and t1.stat3=t2.stat3
and t1.row_id+1=t2.row_id