Ratings on a scale of 1 - 4, with 4 being the highest
"Significance" has to do with the article's ability to make an impact in the field, in public policy, or in the lives of people with drug problems.
"Scientific validity" is a measure of the believability of the science - how likely these results are to stand up in the face of replication by other laboratories and authors. Scientific validity is related to the experimental design, numbers of subjects, statistical methods, and conclusions.
Finally, "originality" rates the innovativeness of the idea, the methods, and the conclusions. There are many "me too" papers in science useful for confirming or refuting earlier findings. An original paper, however, stands out because of its uniqueness.