Articles from scholarly, academic, peer-reviewed, and refereed journals are considered highly credible because they have undergone a peer-review process.They are written by people who have studied their subject deeply and have been reviewed by other people with similar expertise and experience. These articles are typically well sourced, including references to past research through footnotes or a reference list at the end of the article.
It's useful to know who funded the research to help determine if there's possible sponsorship bias, which is the tendency for the methods and results of a study to support the interests of the financial sponsor. This information should be provided in the article, though is less common in older articles when publishers didn't require that funding/sponsorship information be included. Also, keep aware of the dates of the studies you're using and include recent research, when possible.
Scholarly articles can be found by using one or more of the following:
Keyword searching across citations, abstracts and full text of articles (even if the full text isn't available to you).
Enhance efficiency by adjusting your Google Scholar settings so that