Source : Webster's Revised Unabridged Dictionary (1913)

Observational \Ob`ser*va"tion*al\, a.
   Of a pertaining to observation; consisting of, or containing,
   observations. --Chalmers.

Source : WordNet®

observational
     adj : relying on observation or experiment; "experimental results
           that supported the hypothesis" [syn: {experimental}, {data-based}]