Most scientific studies, and in particular at the university level, are funded by grants. These grants are designed in such a way as to ask the researcher to find a way to arrive at a particular conclusion. There are very few funded studies that ask the research to follow a path of true empirical data. The observations are already established by the structure of the grant itself. The entire process leads to a biased scientific approach. It is why we can so easily have one study that says product X is bad for you while another will say it is good for you.
I have been involved in numerous grants and headed enough research projects to know that there is tremendous pressure to support preconceived notions as established within the grant, itself. Scientific peer pressure to not rock the boat and university administration pressure to keep the money flowing also supports the bias, as well.