  A key feature of questionable journals is a lack of adequate peer review of
their articles. Content of thus unknown quality may be utilised by unsuspecting
practitioners or incorporated into peer-reviewed research, becoming
legitimised. It is therefore necessary to examine the citation patterns of
articles in questionable journals to understand the impact and reach of
research in questionable journals. Similar research has tended to focus on
authors from low- and middle-income countries. As such, this study investigates
the profile and impact of research in questionable journals by authors in
Germany. Questionable journals were identified by matching journals with
articles by authors at German institutions from Dimensions to Cabell's
Predatory Reports. Metadata for these articles and a comparative sample of
articles in non-questionable journals were extracted from Dimensions and the 3
year citations, self-citations, uncited rate, profile of co-authoring and
citing countries, and institution type of authors were compared between groups.
Nearly 600 articles in 88 questionable journals were published by German
authors in 2010-2020. Three-quarters were in the medical and health sciences.
Medical articles in questionable journals received significantly fewer
citations than similar articles in non-questionable journals. However, articles
in questionable journals were still extensively cited in 1,736 primarily
non-questionable journals. Self-citations accounted for only 12% of these
citations. Authors from non-university medical facilities were over-represented
in articles in questionable journals. System-level changes are necessary to
eliminate questionable journals and shift high-quality research into reputable
venues.
