Abstract. Planktonic foraminifera are widely used in biostratigraphic,
palaeoceanographic and evolutionary studies, but the strength of many
study conclusions could be weakened if taxonomic identifications are not
reproducible by different workers. In this study, to assess the relative
importance of a range of possible reasons for among-worker disagreement in
identification, 100 specimens of 26 species of macroperforate planktonic
foraminifera were selected from a core-top site in the subtropical Pacific
Ocean. Twenty-three scientists at different career stages – including some
with only a few days experience of planktonic foraminifera – were asked to
identify each specimen to species level, and to indicate their confidence in each
identification. The participants were provided with a species list and had
access to additional reference materials. We use generalised linear
mixed-effects models to test the relevance of three sets of factors in
identification accuracy: participant-level characteristics (including
experience), species-level characteristics (including a participant's
knowledge of the species) and specimen-level characteristics (size,
confidence in identification). The 19 less experienced scientists achieve a
median accuracy of 57 %, which rises to 75 % for specimens they are
confident in. For the 4 most experienced participants, overall accuracy is
79 %, rising to 93 % when they are confident. To obtain maximum
comparability and ease of analysis, everyone used a standard microscope with
only 35× magnification, and each specimen was studied in isolation.
Consequently, these data provide a lower limit for an estimate of
consistency. Importantly, participants could largely predict whether their
identifications were correct or incorrect: their own assessments of
specimen-level confidence and of their previous knowledge of species concepts
were the strongest predictors of accuracy.