Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Randomized Controlled Trial
, 12, 44

Results From a Blind and a Non-Blind Randomised Trial Run in Parallel: Experience From the Estonian Postmenopausal Hormone Therapy (EPHT) Trial

Affiliations
Randomized Controlled Trial

Results From a Blind and a Non-Blind Randomised Trial Run in Parallel: Experience From the Estonian Postmenopausal Hormone Therapy (EPHT) Trial

Piret Veerus et al. BMC Med Res Methodol.

Abstract

Background: The Estonian Postmenopausal Hormone Therapy (EPHT) Trial assigned 4170 potential participants prior to recruitment to blind or non-blind hormone therapy (HT), with placebo or non-treatment the respective alternatives. Before having to decide on participation, women were told whether they had been randomised to the blind or non-blind trial. Eligible women who were still willing to join the trial were recruited. After recruitment participants in the non-blind trial (N = 1001) received open-label HT or no treatment, participants in the blind trial (N = 777) remained blinded until the end of the trial. The aim of this paper is to analyse the effect of blinding on internal and external validity of trial outcomes.

Methods: Effect of blinding was calculated as the hazard ratio of selected chronic diseases, total mortality and all outcomes. For analysing the effect of blinding on external validity, the hazard ratios from women recruited to the placebo arm and to the non-treatment arm were compared with those not recruited; for analysing the effect of blinding on internal validity, the hazard ratios from the blind trial were compared with those from the non-blind trial.

Results: The women recruited to the placebo arm had less cerebrovascular disease events (HR 0.43; 95% CI: 0.26-0.71) and all outcomes combined (HR 0.76; 95% CI: 0.63-0.91) than those who were not recruited. Among women recruited or not recruited to the non-treatment arm, no differences were observed for any of the outcomes studied.Among women recruited to the trial, the risk for coronary heart disease events (HR 0.77; 95% CI: 0.64-0.93), cerebrovascular disease events (HR 0.66; 95%CI: 0.47-0.92), and all outcomes combined (HR 0.82; 95% CI: 0.72-0.94) was smaller among participants in the blind trial than in the non-blind trial. There was no difference between the blind and the non-blind trial for total cancer (HR 0.95; 95% CI: 0.64-1.42), bone fractures (0.93; 95% CI: 0.74-1.16), and total mortality (HR 1.03; 95% CI: 0.53-1.98).

Conclusions: The results from blind and non-blind trials may differ, even if the target population is the same. Blinding may influence both internal and external validity. The effect of blinding may vary for different outcome events.

Trial registration: [ISRCTN35338757].

Figures

Figure 1
Figure 1
EPHT Trial flow chart.
Figure 2
Figure 2
All outcomes: effect of recruitment on control arms.
Figure 3
Figure 3
All outcomes: effect of recruitment on HT arms.

Similar articles

See all similar articles

Cited by 4 articles

References

    1. Godwin M, Ruhland L, Casson I, MacDonald S, Delva D, Birthwhistle R, Lam M, Seguin R. Pragmatic controlled clinical trials in primary care: the struggle between external and internal validity. BMC Med Res Methodol. 2003;3:28. doi: 10.1186/1471-2288-3-28. - DOI - PMC - PubMed
    1. Altman DG. Randomisation. BMJ. 1991;302:1481–1482. doi: 10.1136/bmj.302.6791.1481. - DOI - PMC - PubMed
    1. Altman DG, Bland JM. Treatment allocation in controlled trials: why randomise? BMJ. 1999;318:1209. - PMC - PubMed
    1. Day SJ, Altman DG. Blinding in clinical trials and other studies. BMJ. 2000;321:504. doi: 10.1136/bmj.321.7259.504. - DOI - PMC - PubMed
    1. The CONSORT Statement. http://www.consort-statement.org/consort-statement/ (accessed April 14, 2011)

Publication types

Associated data

LinkOut - more resources

Feedback