corner
Healthy Skepticism
Join us to help reduce harm from misleading health information.
Increase font size   Decrease font size   Print-friendly view   Print
Register Log in

Healthy Skepticism Library item: 14747

Warning: This library includes all items relevant to health product marketing that we are aware of regardless of quality. Often we do not agree with all or part of the contents.

 

Publication type: Journal Article

Chan A, Hróbjartsson A, Jørgensen KJ, Gøtzsche PC, Altman DG.
Discrepancies in sample size calculations and data analyses reported in randomised trials: comparison of publications with protocols
BMJ. 2008 Dec 4; 337:
http://www.bmj.com/cgi/content/abstract/337/dec04_1/a2299


Abstract:

Objective To evaluate how often sample size calculations and methods of statistical analysis are pre-specified or changed in randomised trials.
Design Retrospective cohort study.

Data source Protocols and journal publications of published randomised parallel group trials initially approved in 1994-5 by the scientific-ethics committees for Copenhagen and Frederiksberg, Denmark (n=70).

Main outcome measure Proportion of protocols and publications that did not provide key information about sample size calculations and statistical methods; proportion of trials with discrepancies between information presented in the protocol and the publication.

Results Only 11/62 trials described existing sample size calculations fully and consistently in both the protocol and the publication. The method of handling protocol deviations was described in 37 protocols and 43 publications. The method of handling missing data was described in 16 protocols and 49 publications. 39/49 protocols and 42/43 publications reported the statistical test used to analyse primary outcome measures. Unacknowledged discrepancies between protocols and publications were found for sample size calculations (18/34 trials), methods of handling protocol deviations (19/43) and missing data (39/49), primary outcome analyses (25/42), subgroup analyses (25/25), and adjusted analyses (23/28). Interim analyses were described in 13 protocols but mentioned in only five corresponding publications.

Conclusion When reported in publications, sample size calculations and statistical methods were often explicitly discrepant with the protocol or not pre-specified. Such amendments were rarely acknowledged in the trial publication. The reliability of trial reports cannot be assessed without having access to the full protocols.

 

  Healthy Skepticism on RSS   Healthy Skepticism on Facebook   Healthy Skepticism on Twitter

Please
Click to Register

(read more)

then
Click to Log in
for free access to more features of this website.

Forgot your username or password?

You are invited to
apply for membership
of Healthy Skepticism,
if you support our aims.

Pay a subscription

Support our work with a donation

Buy Healthy Skepticism T Shirts


If there is something you don't like, please tell us. If you like our work, please tell others.

Email a Friend








...to influence multinational corporations effectively, the efforts of governments will have to be complemented by others, notably the many voluntary organisations that have shown they can effectively represent society’s public-health interests…
A small group known as Healthy Skepticism; formerly the Medical Lobby for Appropriate Marketing) has consistently and insistently drawn the attention of producers to promotional malpractice, calling for (and often securing) correction. These organisations [Healthy Skepticism, Médecins Sans Frontières and Health Action International] are small, but they are capable; they bear malice towards no one, and they are inscrutably honest. If industry is indeed persuaded to face up to its social responsibilities in the coming years it may well be because of these associations and others like them.
- Dukes MN. Accountability of the pharmaceutical industry. Lancet. 2002 Nov 23; 360(9346)1682-4.