• The objective of most comparative trials is to show a "positive" result whereby one treatment is significantly better than another. However, the motivation behind some trials is to demonstrate a "negative" result that two treatments are equally effective. Such "equivalence" trials usually arise in comparing a new conservative treatment with an effective but more intensive standard therapy that has potential adverse side effects. Retrospective sample-size tables were provided to determine whether a completed study showing no significant difference between treatment effects is large enough to justify a true-negative conclusion. In this article, the sample sizes given in the decision-making tables are compared with those derived using a confidence-interval approach, the method we recommend for interpreting completed trials in order to judge the range of true treatment differences that is reasonably consistent with the observed data. Some implications of this comparison are discussed in respect to the interpretation of negative studies. Selected biostatistical principles involving the proper use of the tables are also presented. Finally, we distinguish between a completed negative study and an equivalence study, which is designed from the onset to demonstrate the comparability of different treatments. Important design considerations and sample-size tables are given for planning equivalence trials. We show that very large numbers of patients are usually needed to establish with a high degree of confidence that two treatments have comparable efficacy.
(Arch Intern Med 1986;146:986-989)
Thank you for submitting a comment on this article. It will be reviewed by JAMA Internal Medicine editors. You will be notified when your comment has been published. Comments should not exceed 500 words of text and 10 references.
Do not submit personal medical questions or information that could identify a specific patient, questions about a particular case, or general inquiries to an author. Only content that has not been published, posted, or submitted elsewhere should be submitted. By submitting this Comment, you and any coauthors transfer copyright to the journal if your Comment is posted.
* = Required Field
Disclosure of Any Conflicts of Interest*
Indicate all relevant conflicts of interest of each author below, including all relevant financial interests, activities, and relationships within the past 3 years including, but not limited to, employment, affiliation, grants or funding, consultancies, honoraria or payment, speakers’ bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued. If all authors have none, check "No potential conflicts or relevant financial interests" in the box below. Please also indicate any funding received in support of this work. The information will be posted with your response.
Some tools below are only available to our subscribers or users with an online account.
Download citation file:
Web of Science® Times Cited: 37
Customize your page view by dragging & repositioning the boxes below.
More Listings atJAMACareerCenter.com >
Enter your username and email address. We'll send you a link to reset your password.
Enter your username and email address. We'll send instructions on how to reset your password to the email address we have on record.
Athens and Shibboleth are access management services that provide single sign-on to protected resources. They replace the multiple user names and passwords necessary to access subscription-based content with a single user name and password that can be entered once per session. It operates independently of a user's location or IP address. If your institution uses Athens or Shibboleth authentication, please contact your site administrator to receive your user name and password.