Need help evaluating your sources? Use the acronym, ACT UP, to determine whether or not a resource is right for you.
There are several avenues worth exploring to get at research that is not represented in our databases due to privilege in publishing. Open Access Journals can be a really great resource. Open Access (OA) Publishing is free and allows access to anyone. This means research is not hidden behind and expensive pay wall. Keep in mind that not every Open Access Journal is on the up and up. There are scams and shoddy research/reviews that get published in some OA journals. But there are ways for you to evaluate those OA journals
Another avenue is to find scholarly blogs. Oftentimes professors and researchers are talking about their work on blog sites. Just like with any other resource, you will need to evaluate the blog to see if it is credible or not. Here is a website to help you do that
Generally we say, the higher the cited by number is, the more impactful the research is. It means that, in this case, over 3300 articles referenced this particular paper. Considering it was published in 1998, that's a good amount of cited bys as it has had time to be read and thoroughly studied.
But what if I told you that this article was retracted in 2010 for fraudulent research? And that even though it was retracted, it has already been cited over 3300 times and is now part of public discourse. That this particular scholarly article was based on shoddy research and literally started the anti-vax movement?
Who you cite matters! We have a responsibility to thoroughly evaluate our sources.