Related Experiment Video
Updated: Jun 11, 2026

The Adjuvant Efficacy of Angong Niuhuang Pill in the Treatment of Viral Encephalitis: A Meta-Analysis of Randomized Controlled Trials
Published on: April 19, 2024
Meta-analyses of small numbers of trials often agree with longer-term results
Peter Herbison1, Jean Hay-Smith, William J Gillespie
1Department of Preventive and Social Medicine, University of Otago, P.O. Box 913, Dunedin 9054, New Zealand. peter.herbison@otago.ac.nz
Objective:
Many systematic reviews include only a few studies. It is unclear whether recommendations based on these will be correct in the longer term; hence, this article explores whether meta-analyses give reliable results after only a few studies.
Study Design And Setting:
Cumulative meta-analysis of data from 65 meta-analyses from 18 Cochrane systematic reviews was carried out. Various measures of closeness to the pooled estimate from all trials after three and five trials were included. Changes during the accumulation of evidence were noted.
Results:
The 95% confidence interval included the final estimate in 72% of meta-analyses after three studies and in 83% after five studies. It took a median of four (interquartile range: 1.25-6) studies to get within 10% of the final point estimate. Agreement between the results at three and five studies and the final estimate was not predicted by the number of participants, the number of events, τ(2), or I(2). Estimates could still change substantially after many trials were included.
Conclusion:
Many of the conclusions drawn from systematic reviews with small numbers of included studies will be correct in the long run, but it is not possible to predict which ones.
Related Concept Videos
Longitudinal Research
Regression Toward the Mean
Clinical Trials
There are four phases in a clinical trial. A phase one...
Longitudinal Studies
Testing a Claim about Population Proportion
There are two methods of testing a claim about a population proportion: (1) Using the sample proportion from the data where a binomial distribution is approximated to the normal distribution and (2) Using the binomial probabilities calculated from the data.
The first method uses normal distribution as an approximation to the binomial distribution. The requirements are as follows: sample size is large...
Clinical Trials: Overview