Full title of this Texas A&M study is: An Evaluation of Improper Refrigerant Charge on the Performance of a Split System Air Conditioner with Capillary Tube Expansion by Mohsen Farzad and Dennis L. O'Neal. It investigates the effect of improper charging on the performance of a residential air conditioner.
This article is from the National Institute of Standards and Technology, part of The US Dept of Commerce. The last two paragraphs of section 2.1 are powerful and show that 95% of residential systems checked in a large survey failed the efficiency test because they were installed incorrectly.
Collateral on the number of systems that are improperly charged. From the article: "recent field studies suggest that approximately 75% of installed cooling equipment may have incorrect amount of refrigerant. Incorrect refrigerant level can lower efficiency by 5 to 20% and can ultimately cause premature component failure, resulting in costly repairs that could have been prevented."