Evaluations can be flawed by evaluators who relentlessly insist on answering the original questions, regardless of intervening events, changes in the object of the evaluation, or new discoveries. During the course of an evaluation, many occurrences一for example, changes in scheduling, personnel, and funding; unanticipated problems in program implementation; evaluation procedures that are found not to work; lines of inquiry that prove to be dead ends; new critical issues that emerge-require new or revised evaluation questions. Because such changes cannot be foreseen, Cronbach and his associates ( 1980) propose that: