Results
There were 88 papers (39.5%) with a prospective study design while 43
(19.3%) and 92 (41.2%) papers had a case-control and cross-sectional
design, respectively. Amongst all included papers, 45.4% fully reported
all 22 STROBE items according to our conservative definition or by
citation. This differed by study type with 47.8% for cohort studies,
45.7% for cross-sectional studies, and 41.4% for case-control studies
(pChiSq=0.007 for the overall comparison of the three
designs). This difference was brough about by the case-control studies
which differed from cohort (pChiSq=0.0017) and
cross-sectional studies (pChiSq=0.035); the difference
between cohort and cross-sectional studies was not statistically
significant. This difference by study design remains when using our
liberal scoring of the 22 STROBE items or reporting by citation. Here,
we observed 67.0% for cohort studies, 64.1% for cross-sectional
studies, and 58.1% for case-control studies
(pChiSq<0.0001 and
pChiSq=0.0015 comparing case-control to cohort and to
cross-sectional studies, respectively;
pChiSq<0.0001 for the overall comparison of
the three designs; no statistically significant difference between
cohort and cross-sectional studies).
A clear difference between our conservative and liberal scoring
definitions to the STROBE checklist was observed for the title and
abstract sections. This was due to the low proportion of papers
reporting their study design in the title or abstract (28.3%). Of note,
this proportion was higher for cohort studies and cross-sectional
studies (36.4% and 33.7%, respectively) than for case-control studies
(18.6%). The percentages of full reporting by item, paper section, and
study design are shown in figure 1.
The overall score was stable over time, irrespective of our conservative
or liberal definition. Investigating sections of the STROBE, we observed
that funding reporting increased from less than 60% to more than 90%
while the scoring for other STROBE sections remained rather constant
over the period from 2009 to 2018 (Fig 2).
Finally, results from the correspondence analyses show that its first
two dimensions together explain 29.6% and 36.9% of the overall
variance in our conservative and liberal STROBE scores, respectively.
The first dimension separates full reporting from “not reported”,
explaining 18.6% and 23.9% of the overall variance in our conservative
and liberal scores, respectively. The positioning of study designs along
this dimension shows that reporting in papers based on a cohort study
was more complete than reporting in papers based on a case-control
design; here, the cross-sectional studies had an intermediate position.
For the conservative score, the second dimension separated the STROBE
items 1, 4, 7-11, 14, 17, and 21 from the other STROBE items. Notably,
those items investigate reporting of features of the study design in the
title and methods, of types of variables and their
measurement/assessment, of bias and confounding, of study size, and of
grouping of variables. These items are also the more often poorly
reported ones. In the correspondence analysis of our liberal score, this
cluster is extended to the items 6, 9, 10, and 12 from the methods
section, 16 and 19 from the results section, and item 22 regarding the
funding source. In essence, the second dimension separates items from
the methods and results sections with low proportion of full reporting
from the other STROBE items. Again, positioning of the study designs
along this dimension separates cohort and cross-sectional designs from
case-control studies confirming the aforementioned poor reporting in
papers based on a case-control design.