So the research that established the placebo effect—an effect that’s well-known, and widely regarded as an illustration of the importance of control groups in research—itself had no control group? That’s incredible.
Here's an excerpt:
>We included randomised placebo trials with a no-treatment control group investigating any health problem
That article's more recent (2010) link supports its conclusion, which wouldn't need to be stated unless it contrasted with what it calls “pharmacological folklore” from the original publication, which the author says he “took literally” for many decades after.
The point being that the 1955 version of the idea is currently much more widely known than modern no-treatment comparisons, and most people don't realize that its research basis is so flimsy.
[1] https://books.google.com/ngrams/graph?content=placebo+effect...