In 2015, a group of researchers from the United States published a study looking at the potential of the drug ketamine to treat people with bipolar disorder. For the work they bundled together previously published papers on the topic into what’s called a meta-analysis — a type of study that’s designed to sift through differences across multiple trials to get at a true effect. Trouble was, the researchers made a major blunder: Three of the five studies included many of the same patients, a fact the authors failed to identify. Double counting of results is a serious concern for scientists because it can inflate the apparent benefits (or risks) of a particular therapy. In this case, it made ketamine seem to be a “significantly effective” treatment for depression. The authors of the meta-analysis, which appeared in the Journal of Psychiatric Practice, said the error — which a pair of scientists in Sweden discovered — was inadvertent and that they are reworking their study with the correct data. In the meantime, they’ve retracted the paper.