Anecdotal
Etymology
From Greek "anekdota," "things unpublished," from "an-" ("not") and "ekdotos" ("given out, published"). The historian Procopius titled his secret memoirs the "Anecdota." As those loose, unofficial tales came to be called anecdotes, the adjective attached to the kind of casual, story-based evidence they represent.
adjective · /an-ik-DOH-tul/
Based on personal stories or isolated cases rather than systematic evidence.
What it names
A gentle warning label: use it when someone reasons from "my cousin tried it and it worked," where the sample is a story or two, not a study.
Example
The support for the supplement was entirely anecdotal — glowing reviews, but no controlled trials.
Related idea
The counterpart to empirical: empirical evidence is gathered and measured deliberately, while anecdotal evidence is accumulated by chance from individual accounts.