When dealing with humans, the likely answer is that the relationship is far more complex and based on variable that are beyond our ability to adequately grasp and measure. So what appears to be the same study done multiple times can get different results. As time progresses, social change can lead to what was once consistent result of outcome A becoming inconsistent results and eventually becoming consistent results of outcome B.
Also, many studies are done primarily on college students, so trends that may well be true for them may not apply to the general population. So as studies become better at getting a representative cross section of the population results can appear to change despite early studies being correct.
A large part of this is that results are extremely overstated in the social sciences. If not by the scientists, then by the media and popular culture.
Also, many studies are done primarily on college students, so trends that may well be true for them may not apply to the general population. So as studies become better at getting a representative cross section of the population results can appear to change despite early studies being correct.
A large part of this is that results are extremely overstated in the social sciences. If not by the scientists, then by the media and popular culture.