A Boolean, or logical, variable is one that can take the values T (true) or F (false); and the Boolean, or logical, algebra pioneered by George Boole (1815–1864) holds the formal machinery that allows such truth values to be logically combined. Boolean principles offer a framework for handling questionnaire and symptom data of the common binary kind (yes vs. no, normal [“negative”] vs. abnormal [“positive”], etc.), for clinical decisions, even measurements, probabilities, and so on, often have to be dichotomized (binarized). Library searches exploit Boolean AND, OR, and NOT, and the digital computer is essentially a huge number of electronic switches (on vs. off) connected in a Boolean manner, marching to the beat of a clock. Boolean principles also underlie logical checking of rule-based decision ...