Evidence that enables a psychologist to create knowledge may not be sufficient if scientists are constantly assuming that there is a single cause for every human behaviour. This was proven to be the case when Cullen et al. replicated Aronson’s study in the UK and found that stereotype threat actually had very slight impact outside a laboratory setting (Cullen). The problem with Aronson’s study was that his study only looked at a very narrow population and culture and may have disregarded countless numbers of other variables that may have played a role. Hence, we can speculate that psychologists are naturally inclined to avoid complexity and this may influence how psychologists perceive information.However, it is important to note that without Aronson’s assumption that there was some kind of pattern – that there was a rational cause behind the students’ performances on exams in the first place – he would not have found out what he found, nor would have Cullen. Although a theory may be false or may only cover a small percentage of a broad spectrum of explanations, until it is falsified, we can still call it knowledge because in fact, knowledge is what allows us to make sense of the world. So, is assuming uniformity simply our desire to establish a common cause, is it necessary?Without the assumption that results from a study can be extrapolated to the world, psychologists cannot predict therefore, psychology makes no progress. Assuming uniformity itself is a hypothesis that can be tested and does not need to be able to produce knowledge of complete certainty. Even though Aronson’s theory was later challenged by Cullen, it still allowed scientists try to make sense of what was happening around them. The assumption of uniformity is necessary in the sciences to permit progress and any iterative research, whether or not psychologists are imposing uniformity into the world.