Are we talking cigarettes?  water? coffee? other?   Yes, other.   In this case about what is sometimes called “filtered” or “unfiltered” literature in the evidence-based medicine pyramid of research evidence.  (I have more than one issue with this particular pyramid as a representation of all evidence, but for right now let’s look at filtered information & unfiltered information.  Pyramid source:  Wikimedia Commons  

Filtered is considered stronger–meaning that we can be more confident that literature from this category better  supports cause and effect.  I agree.

Unfiltered evidence (usually single studies etc) is considered weaker–meaning that we must be more cautious about its accuracy in representing reality.  I agree.

But, “Is unfiltered information really unfiltered?”  No filtering at all? My qualified answer is, “No.”   Argue with me if you like.

My opinion: If the “unfiltered” article is a primary source, research study that has strong design and is published in a peer-review journal then it has been filtered by multiple, expert peer reviewers just to make it to publication.

Thus, when discussing filtered vs. unfiltered one should be very clear on what those terms mean and do not mean.

Critical Thinking: When filtered literature (systematic reviews & critically appraised topics & articles) has been filtered by one individual, is that superior to unfiltered literature in terms of introducing bias?  What if the “filtered” evidence is 7 years old and a primary, “unfiltered” source(s) from this year has different findings?   What is the relationship between “filtered” and “unfiltered”–after all the “unfiltered” is the pyramid base so what does that mean?

For more Info:  For peer review, the lower level filtering of single studies, consider its 1)  advantages (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4975196/)  and 2) its potential flaws (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1420798/)