Do double-blind studies with informed consent yield externally valid results? An empirical test.

  • Kirsch I
  • Rosadino M
  • 26


    Mendeley users who have this article in their library.
  • 58


    Citations of this article.


Subjective and physiological effects of caffeine were investigated via a 3 x 2 x 3 design that assessed independent and interactive effects of instructions (told caffeine versus told no caffeine versus not told whether beverage contained caffeine), actual beverage content (caffeine versus no caffeine), and time after ingestion (15, 30, and 45 min). Instructions affected alertness at 15 min after ingestion. Caffeine increased alertness at 30 min after ingestion and systolic blood pressure at 30 min and 45 min after ingestion. A highly significant instruction by drug interaction on tension was obtained at all measurement points, indicating an increase in tension only among subjects who knowingly received caffeine. Because people are generally informed of drug content in non-research settings, these data challenge the external validity of typical double-blind studies, in which subjects are informed of the possibility of receiving a placebo as part of the consent procedure.

Author-supplied keywords

  • blind design - informed
  • caffeine - placebo -
  • consent
  • expectancy

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document

Get full text


  • Irving Kirsch

  • Michael J. Rosadino

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free