The issue focused on is that not all published studies are produced by the same method of analysis. It is very possible that more than one method of analysis was used to produce the same result. It is also possible that not all published studies are published in the same journal. It is also possible that not all published studies are published in the same language. It is also possible that not all published studies are published in the same research field. It is also possible that not all published studies are published in the same research field