Quality of reporting of confounding remained suboptimal after the STROBE guideline.
OBJECTIVE
Poor quality of reporting of confounding has been observed in observational studies prior the STrenghtening the Reporting of Observational studies in Epidemiology (STROBE) statement, a reporting guideline for observational studies. We assessed whether the reporting of confounding improved after the STROBE statement.


METHODS
We searched MEDLINE for all articles about observational cohort and case-control studies on interventions with a hypothesized beneficial effect in five general medical and five epidemiologic journals published between January 2010 and December 2012. We abstracted data for the baseline period before the publication of the STROBE statement (January 2004-April 2007) from a prior study. Six relevant items related to confounding were scored for each article. A comparison of the median number of items reported in both periods was made.


RESULTS
In total, 174 articles published before and 220 articles published after the STROBE statement were included. The median number reported items was similar before and after the publication of the STROBE statement [median, 4; interquartile range [IQR], 3-5 vs. median, 4; IQR, 3.75-5]. However, the distribution of the number of reported items shifted somewhat to the right (P = 0.01).


CONCLUSIONS
Although the quality of reporting of confounding improved in certain aspects, the overall quality remains suboptimal.
Unit of PharmacoEpidemiology and PharmacoEconomics, Department of Pharmacy, University of Groningen, Antonius Deusinglaan 1, XB45, Groningen 9713 AV, The Netherlands. Electronic address: k.b.pouwels@gmail.com.
Koen B
KB
Pouwels
Unit of PharmacoEpidemiology and PharmacoEconomics, Department of Pharmacy, University of Groningen, Antonius Deusinglaan 1, XB45, Groningen 9713 AV, The Netherlands.
Niken N
NN
Widyakusuma
Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Universiteitsweg 100, Utrecht 3584 CX, The Netherlands.
Rolf H H
RH
Groenwold
Unit of PharmacoEpidemiology and PharmacoEconomics, Department of Pharmacy, University of Groningen, Antonius Deusinglaan 1, XB45, Groningen 9713 AV, The Netherlands; Department of Epidemiology, University Medical Center Groningen, University of Groningen, Hanzeplein 1, Postbus 30 001, Groningen 9700 RB, The Netherlands.
Eelko
E
Hak
D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D006801:Humans; D064887:Observational Studies as Topic; D017410:Practice Guidelines as Topic; D012107:Research Design / Q000592:standards*
Confounding factors; Editorial policies; Epidemiology; Guideline adherence; Guidelines as topics; Publishing/standards