Placebo vs Blinding
Both terms below come up in the same part of the course, and students mix them up. Here is each one defined on its own, side by side, so you can see where they part company.
Placebo
Collecting data and study design
A placebo is a dummy treatment with no active ingredient, given so a group's experience matches the real treatment except for the component being tested.
A placebo controls for the placebo effect, the tendency of people to respond simply because they believe they are being treated. A sugar pill, saline injection, or sham procedure looks and feels like the real thing but does nothing on its own. For example, in a drug trial the control group takes an identical-looking sugar pill so both groups share the same expectations. Any difference in outcomes between the groups can then be credited to the drug's active ingredient rather than to belief.
Blinding
Collecting data and study design
Blinding keeps people in an experiment from knowing which treatment a subject received, so their expectations cannot bias the response or its measurement.
Blinding prevents knowledge of the treatment from coloring how subjects respond or how researchers measure outcomes. In a single-blind study the subjects do not know their group; blinding the people who assess results guards against biased scoring. For example, a taster who does not know which cola is brand A rates the flavor on taste alone. Without blinding, expectations can nudge both the response and its measurement toward what people hope to see.