“Standard errors were used instead of standard deviations when using data from one of the studies (Koh et al) included in the meta-analyses,” states the notice.
“Numerous inconsistencies were noted from the numbers used in the meta-analyses when compared to the original studies. All authors agree to this retraction.”
In a similar second retraction notice, both published in the Journal of Human Hypertension, the authors again cited fundamental errors in the data presented that undermined the conclusions drawn.
“Standard error was used instead of the standard deviation from two trials included in the meta-analysis.
“This has seriously affected the overall effect. There have also been other inconsistencies noted in the values used in the calculations from the original studies”
The first papers looked to explore the reductive effect of α-lipoic acid (ALA) supplementation on systolic blood pressure (SBP) and diastolic blood pressure (DBP).
The researchers, which also included colleagues from Iran, concluded in the meta-analysis of randomised controlled trials that ALA supplementation lowered BP in subjects, especially those with elevated BP.
The second paper was a systematic review and meta-analysis of randomised controlled trials and looked to investigate the efficacy of oral L-citrulline supplementation on systolic and diastolic blood pressure.
This paper also concluded that L-citrulline improved systolic and diastolic blood pressure and may be more efficacious in pre-hypertensive and hypertensive populations.
Speaking to RetractionWatch, Sadegh Jafarnejad of Kashan University of Medical Sciences, the corresponding author of both papers, said, “As the retraction notices emphasise, both papers were retracted due to author’s request.”
“After some human errors (honest errors) were found in presented data, we tried to correct the papers by letter to editor/erratum.
“However after consulting with co-authors and Editor, we decided to retract the papers and submit them in the journal after rectifying and revising the data (one is submitted in the same journal and another one will be submitted very soon).”
According to Indiana University’s David Allison, the decision to use either standard deviation or standard error is one that is prone to error due to the similarity in what each term measures.
“Errors in meta-analyses are common,” Allison told RetractionWatch. “In my experience, perhaps the most common error entails miscalculation of the effect size and what seems to be the most common source of this miscalculation is misapprehension of some measure of variance.
“Mistaking a standard error for a standard deviation is common and seems to often result from a combination of insufficient carefulness on the part of the meta-analysts and unclear or incorrect labelling of standard errors vs standard deviations in the original articles being meta-analysed.
“Unfortunately, such errors can invalidate a meta-analysis.”