What defines a peer reviewed paper from a credible scientific journal isn't really a matter of opinion. What it means is that a panel of people who are recognized as experts in the field that the paper is on, or a related field, has reviewed the paper. They evaluate the overall goal, if they believe that it isn’t in depth or rigorous study then they reject it. They evaluate the methodology to ensure that bias is minimized or eliminated; they check and evaluate the results and conclusions. They ensure that the claims made in the conclusions are supported by the data gathered in the study and that it expands the body of knowledge of the particular field.