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Content: Hence operational definitions must be known precisely, to replicate research. What are common reasons a replication fails? If a replication fails, that does not imply somebody lied or cheated. Most scientists are honest. Most failures of replication are due to differences in how the research was performed. Possible differences include: the subjects involved (Nationality? Age? Volunteers or paid subjects?) the time of day, the weather, the expectations of the experimenter (a powerful effect), and many other variables.