The phrase "able to observe the effect of" is correct and usable in written English.
You can use it when discussing the capability to notice or perceive the impact of a particular action, event, or phenomenon.
Example: "In the experiment, we were able to observe the effect of temperature on the reaction rate."
Alternatives: "capable of noticing the impact of" or "able to perceive the influence of".
Since we have telescopes that can look at the universe when it was younger, we would be able to observe the effect of time going slower in the early universe, if we had the ability to look back that far.
The layers are situated in the unsaturated zone near the watertable and they are inclined to be able to observe the effect of discontinuities in capillary forces and relative permeabilities.
Algal concentrations were deliberately chosen to differ from concentrations of previous experiment so as to be able to observe the effect of these algal concentrations as well.
But in studying the agents -- a suggestion from her husband -- "we are able to use ambulatory blood pressure monitors to observe the effects of real-life conflicts under relatively consistent circumstances," she said.
Greenland is one of the best places to observe the effects of climate change.
Medical students have studied her hands to observe the effects of such extreme arthritis.
His service allowed him to observe the effects of scurvy at first hand.
Scientists were trying to observe the effects of the viruses and to develop new treatments.
And, because of the duel-like intimacy of snooker, O'Sullivan is able to observe the mesmerizing effect that his skill has on his opponents: "You're thinking, 'You've got that on a string, mate.
Accordingly, if administered early enough (as early as 1 week hyperglycemia) we may be able to observe the beneficial effects and prevention of nerve damage.
We were also able to observe the country-specific effects of the measurement invariance assumption on the prediction validity of the GLMM's random slope coefficients.
