LNSLNS Correct extraction of the relevant data from the original publications in the summaries is of the utmost importance. Mistakes or a lack of careful scrutiny can crucially skew the results. As described in our checklist, written inclusion and exclusion criteria that are -defined a priori in the study protocol have to be taken into consideration in this regard (1). This means for example that the surgical techniques that were included in the summary have to be defined with precision. Multiple publications of the same study group are not a rare event, and the exclusion criteria have to be set in such a way as to exclude such publications. What is also useful is quality assurance of the included studies by means of quality criteria that are defined a priori (2) or by means of a quality score (3). This enables the authors of the summary to assess the included data more thoroughly, and it enables reviewers and readers to do the same.

As with all original articles, the team of researchers is duty bound to ensure careful and correct data extraction. Ideally, for a summary, the literature search, data extraction, and data evaluation should be done in parallel by two independent persons. If this is not possible then, at least a second person should check everything carefully and verify what was done. Another option for checking the quality of the summary is to conduct an independent audit of the research team.

Reviewers of scientific journals cannot replicate the entire work done by the researchers, but by checking manuscripts carefully they can detect errors and weaknesses while gaining an impression of how carefully the work has actually been done. Finally, educated readers, whom we have provided with a checklist and an understanding of the problems, will be able to judge the quality of a summary.
DOI: 10.3238/arztebl.2010.0057b

Dr. med. Meike Ressing
PD Dr. rer. nat. et med. habil. Stefanie J. Klug, MPH
Institut für Medizinische Biometrie, Epidemiologie und Informatik (IMBEI)
Universitätsmedizin der Johannes Gutenberg-Universität Mainz
Obere Zahlbacher Str. 69, 55101 Mainz, Germany
klug@imbei.uni-mainz.de

Conflict of interest statement
The authors of all contributions declare that no conflict of interest exists according to the guidelines of the International Committee of Medical Journal Editors.
1.
Ressing M, Blettner M, Klug SJ: Systematic literature reviews and meta-analyses—Part 6 of a Series on Evaluation of scientific publications. [Systematische Übersichtsarbeiten und Metaanalysen – Teil 6 der Serie zur Bewertung wissenschaftlicher Publikationen]. Dtsch Artzebl Int 2009; 106: 456–63 VOLLTEXT
2.
Klug SJ, Ressing M, Koenig J, Abba MC, Agorastos T, Brenna SM, et al.: TP53 codon 72 polymorphism and cervical cancer: a pooled analysis of individual data from 49 studies. Lancet Oncol 2009 Aug; 10(8): 772–84 MEDLINE
3.
Klug SJ, Hukelmann M, Blettner M: Knowledge about infection with human papillomavirus: A systematic review. Prev Med 2008 Feb; 46(2): 87–98 MEDLINE
1. Ressing M, Blettner M, Klug SJ: Systematic literature reviews and meta-analyses—Part 6 of a Series on Evaluation of scientific publications. [Systematische Übersichtsarbeiten und Metaanalysen – Teil 6 der Serie zur Bewertung wissenschaftlicher Publikationen]. Dtsch Artzebl Int 2009; 106: 456–63 VOLLTEXT
2. Klug SJ, Ressing M, Koenig J, Abba MC, Agorastos T, Brenna SM, et al.: TP53 codon 72 polymorphism and cervical cancer: a pooled analysis of individual data from 49 studies. Lancet Oncol 2009 Aug; 10(8): 772–84 MEDLINE
3. Klug SJ, Hukelmann M, Blettner M: Knowledge about infection with human papillomavirus: A systematic review. Prev Med 2008 Feb; 46(2): 87–98 MEDLINE