In addition to being relevant to practitioners, articles in Financial Analysts Journal are required to meet high standards of academic excellence. As a byproduct, readers are frequently faced with terms such as “standard error of the estimate” or “t-test” that—even though possibly studied years ago—are certainly not everyday terms in an investment practitioner’s world. We introduce here a new column designed to provide short “English-language” explanations of “What Practitioners Need to Know.” For our first topic, we have selected t-tests.