We excluded letters, comments, reviews, meta-analyses, ecological studies, and animal studies.
Collectively we refer to these eligible articles as "comment pieces" We excluded letters, views, book reviews and primary research articles.
Finally journal article was selected as "Publication Type" to exclude letters, editorials, news, etc. [ 17].
We included only the first letter for a given new drug or biologics licensing application, thus excluding letters issued after sponsors responded to initial letters by resubmitting applications.
CINAHL Data linkage OR Medical record linkage Limited to years 1991-2007, thEnglishsh Language and studies involving humans EMBASE Data AND Linkage Medical AND Record AND Linkage Limited to years 1991-2007, thEnglishsh Language and studies involving humans, excluding letters, notes, commentaries and editorials.
The fist involved an advanced search in PubMed for journal articles (excluding letters, editorials and other kinds of citations) indexed by the National Library of Medicine experts under the major subject headings (MeSH) shown in figure 1. Citations were retrieved yearly from 1991 up to 2003 and for three income regions: Upper Middle Income (UMI), Lower Middle Income (LMI) and Low Income (LI).
We included only full (peer reviewed) journal publications from corresponding protocols of randomised controlled trials; we excluded research letters, letters to the editor, or conference abstracts.
We excluded the letter to the editor but found the original, peer-reviewed publication and included it in our evidence base.
However, when we excluded the letter fluency test from these models, these inverse associations became more pronounced, most markedly for patella bone lead.
