IDEAS home Printed from
MyIDEAS: Log in (now much improved!) to save this paper

Testing for Placebo Effects Using Data from Blinded, Randomized Controlled Trials

Listed author(s):
  • Anup Malani

This paper proposes a test for the existence of placebo effects, as described by the so-called expectancy theory. This theory, which is the dominant medical theory of how placebo effects operate, posits that health outcomes rise in individuals' beliefs about the probability that they are getting a beneficial treatment and their beliefs about the efficacy of that treatment. Blinded, randomized, controlled trials provide near-perfect environments in which to test this theory because they offer objective, controlled manipulations of subjects' beliefs about treatment. If the expectancy theory is correct, outcomes in trials offering a higher probability of receiving an experimental treatment should be superior to outcomes in trials offering a lower probability of receiving that treatment, conditional on treatment assignment. The paper applies this test to data from over 200 trials of anti-ulcer medications and finds robust evidence of placebo effects in trials of H2-blockers (e.g., Zantac, Tagamet and Pepcid) and of proton-pump inhibitors (e.g., Prilosec, Nexium, and Prevacid). Indeed, trials of H2-blockers manifest placebo effects that are 50 percent as large as the physiological effects of these medications. Because placebo effects are not confined to clinical trials, this result suggests that the standard difference-in-means estimator of treatment effects may seriously underestimate the efficacy of anti-ulcer medications

If you experience problems downloading a file, check if you have the proper application to view it first. In case of further problems read the IDEAS help page. Note that these files are not on the IDEAS site. Please be patient as the files may be large.

File URL:
Download Restriction: no

Paper provided by Econometric Society in its series Econometric Society 2004 North American Summer Meetings with number 104.

in new window

Date of creation: 11 Aug 2004
Handle: RePEc:ecm:nasm04:104
Contact details of provider: Phone: 1 212 998 3820
Fax: 1 212 995 4487
Web page:

More information through EDIRC

References listed on IDEAS
Please report citation or reference errors to , or , if you are the registered author of the cited work, log in to your RePEc Author Service profile, click on "citations" and make appropriate adjustments.:

in new window

  1. Mark Yuying An, 1996. "Log-concave Probability Distributions: Theory and Statistical Testing," Game Theory and Information 9611002, EconWPA.
  2. Heckman, James J & Honore, Bo E, 1990. "The Empirical Content of the Roy Model," Econometrica, Econometric Society, vol. 58(5), pages 1121-1149, September.
Full references (including those not matched with items on IDEAS)

This item is not listed on Wikipedia, on a reading list or among the top items on IDEAS.

When requesting a correction, please mention this item's handle: RePEc:ecm:nasm04:104. See general information about how to correct material in RePEc.

For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: (Christopher F. Baum)

If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

If references are entirely missing, you can add them using this form.

If the full references list an item that is present in RePEc, but the system did not link to it, you can help with this form.

If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your profile, as there may be some citations waiting for confirmation.

Please note that corrections may take a couple of weeks to filter through the various RePEc services.

This information is provided to you by IDEAS at the Research Division of the Federal Reserve Bank of St. Louis using RePEc data.