The Saarbrücken scientists were able to confirm that the hearts of these athletes, who have been engaged in elite level endurance activities for many years, were, as expected, significantly larger and stronger than those of members of the control group. (sciencedaily.com)
But — in a way that could potentially confound the findings — members of the control group in some cases received aid from other organizations. (sciencemag.org)
In every experimental evaluation of private school voucher programs, the students who won the voucher lottery but did not consistently use their voucher to attend private schools have remained in the study over time as members of the treatment group, and the students who lost the voucher lottery but enrolled in private school have remained in the study as members of the control group. (educationnext.org)