To evaluate a plan to save money on office-space expenditures by having its employees work at home, XYZ Company asked volunteers from its staff to try the arrangement for six months. During this period, the productivity of these employees was as high as or higher than before. Which of the following, if true, would argue most strongly against deciding, on the basis of the trial results, to implement the company's plan? ['The volunteers who worked at home were able to communicate with other employees as necessary for performing the work.', "The employees who agreed to participate in the test of the plan were among the company's most self-motivated and independent workers.", 'Other companies that have achieved successful results from work-at-home plans have workforces that are substantially larger than that of XYZ.', 'Minor changes in the way office work is organized at XYZ would yield increases in employee productivity similar to those achieved in the trial.']