Numerical social trends have become increasingly available and useful both for the retrospective examination of social change and for extrapolation and prediction. Five types of social trends are distinguished here: Type A (developmental), Type B (mixed), Type C (motivational). Type D (institutional), and Type E (adversarial). Numerous examples of each type are described. It turns out that when the five types are arrayed in the order of their dependence on scientific-technical progress, their predictive potential falls into the same rank order. Presumably because almost all of that potential is ultimately derived from scientific-technique progress. A sixth type of trend—virtually independent of science-technology and highly resistant to interpretation—is briefly noted.