Trace this claim back to its origin

A "studies show" claim that everyone repeats and nobody links.

Help me trace this claim to its origin.

1. What is the earliest source you are aware of for this claim, and how confident are you that it is genuinely the earliest? Say if you are unsure. Do not fabricate a citation, an author, a year, or a title. If you do not know the source, say you do not know and describe what the source would look like.
2. Describe the chain as you understand it: original work, then who cited it, then how the claim changed as it travelled.
3. Identify where the claim drifted from what the original actually said. Citation chains usually lose a qualifier at each hop.
4. Give me exact search strings and the specific places to look to verify this myself.
5. Tell me what I should conclude if the trail goes cold, because that is itself informative.

The claim:

Testing a claim. Statistics, causal stories, methodology, and tracing a repeated claim back to where it started.