Comparison of effectiveness between systems is hampered by different measures of effectiveness being used. Often there is no formal monitoring program, so only anecdotal evidence is available. When there is an active monitoring program the measure of effectiveness often varies.

Direct Mortality (dead bird recoveries from the pond in question) would seemingly be the best most consistent measure of effectiveness, but there are several confounding factors which need to be taken into account.

• Mortality is typically a rare event and often episodic in nature. These "features" make statistical analysis of mortality difficult at best and often impossible.
• In ponds which have heavy salts and low pH values, the feathers are stripped of their waterproofing qualities rather quickly, often in a matter of minutes (pers. obser., pers. com. Lynn Frink., Tri State Bird Rescue Res. Inc.) . Subsequently, The bird becomes encrusted with heavy salt crystals. The added weight combined with the loss of waterproofing lead to the bird being "pulled" under the surface of the water, where the bird drowns (pers. obser.).
• The low pH also leads to the rapid degeneration of the bird carcass, so typically no evidence of the dead bird is found.
• Birds which are effectively hazed off the pond may have ingested a lethal dose of chemicals as the bird tried to rehydrate after a long flight. These birds hazed off the surface after landing have also been subjected to the stripping of waterproof oils and feather fracturing. The result of this loss of insulation can be the death of the bird several miles from the pond which caused the problems.

Because of these problems several alternative methods for quantifying possible bird mortality have been devised. The best of these measures is counts of landings on the contaminated area. For this measure to be accurate however the treatment needs to be applied in a random fashion. In essence numbers of landings during the application of the aversion technique need to be compared to the landings that occur during times when the treatment is not active. This give very good comparative numbers but often it is impractical to repeatedly activate and inactivate a hazing system. The observation phase is also quite long and expensive.

Other methods may not have as much scientific rigor but can and are applied when conditions of a study dictate. Included in this category include observed vs. expected landing ratios, and behavioral observations.

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