Inappropriate use of standard error of the mean when reporting variability of study samples: a critical evaluation of four selected journals of obstetrics and gynecology.
OBJECTIVE
The study was designed to investigate the frequency of misusing standard error of the mean (SEM) in place of standard deviation (SD) to describe study samples in four selected journals published in 2011. Citation counts of articles and the relationship between the misuse rate and impact factor, immediacy index, or cited half-life were also evaluated.


METHODS
All original articles in the four selected journals published in 2011 were searched for descriptive statistics reporting with either mean ± SD or mean ± SEM. The impact factor, immediacy index, and cited half-life of the journals were gathered from Journal Citation Reports Science edition 2011. Scopus was used to search for citations of individual articles. The difference in citation counts between the SD group and SEM group was tested by the Mann-Whitney U test. The relationship between the misuse rate and impact factor, immediacy index, or cited half-life was also evaluated.


RESULTS
The frequency of inappropriate reporting of SEM was 13.60% for all four journals. For individual journals, the misuse rate was from 2.9% in Acta Obstetricia et Gynecologica Scandinavica to 22.68% in American Journal of Obstetrics & Gynecology. Articles using SEM were cited more frequently than those using SD (p = 0.025). An approximate positive correlation between the misuse rate and cited half-life was observed.


CONCLUSIONS
Inappropriate reporting of SEM is common in medical journals. Authors of biomedical papers should be responsible for maintaining an integrated statistical presentation because valuable articles are in danger of being wasted through the misuse of statistics.
Institute of Medicine, Chung-Shan Medical University, Taichung City, Taiwan; Department of Anesthesiology, Chung-Shan Medical University and Chung-Shan Medical University Hospital, Taichung City, Taiwan.
Wen-Ru
WR
Ko
Institute of Medicine, Chung-Shan Medical University, Taichung City, Taiwan; Department of Anesthesiology, Chung-Shan Medical University and Chung-Shan Medical University Hospital, Taichung City, Taiwan.
Wei-Te
WT
Hung
School of Public Health, Chung Shan Medical University, Taichung City, Taiwan; Library and Evidence Based Medicine Center, Chung Shan Medical University Hospital, Taichung City, Taiwan.
Hui-Chin
HC
Chang
Institute of Medicine, Chung-Shan Medical University, Taichung City, Taiwan; Department of Obstetrics and Gynecology, Chung-Shan Medical University and Chung-Shan Medical University Hospital, Taichung City, Taiwan. Electronic address: viola5563@gmail.com.
Long-Yau
LY
Lin
D035843:Biomedical Research / Q000592:standards*; D003627:Data Interpretation, Statistical; D006176:Gynecology; D006801:Humans; D055811:Journal Impact Factor; D009774:Obstetrics; D010506:Periodicals as Topic / Q000592:standards*
impact factor; prescriptive statistics; standard deviation; standard error of the mean; variability of study sample