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Kappa statistic to measure agreement beyond chance in free-response assessments

Overview of attention for article published in BMC Medical Research Methodology, April 2017
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Title
Kappa statistic to measure agreement beyond chance in free-response assessments
Published in
BMC Medical Research Methodology, April 2017
DOI 10.1186/s12874-017-0340-6
Pubmed ID
Authors

Marc Carpentier, Christophe Combescure, Laura Merlini, Thomas V. Perneger

Abstract

The usual kappa statistic requires that all observations be enumerated. However, in free-response assessments, only positive (or abnormal) findings are notified, but negative (or normal) findings are not. This situation occurs frequently in imaging or other diagnostic studies. We propose here a kappa statistic that is suitable for free-response assessments. We derived the equivalent of Cohen's kappa statistic for two raters under the assumption that the number of possible findings for any given patient is very large, as well as a formula for sampling variance that is applicable to independent observations (for clustered observations, a bootstrap procedure is proposed). The proposed statistic was applied to a real-life dataset, and compared with the common practice of collapsing observations within a finite number of regions of interest. The free-response kappa is computed from the total numbers of discordant (b and c) and concordant positive (d) observations made in all patients, as 2d/(b + c + 2d). In 84 full-body magnetic resonance imaging procedures in children that were evaluated by 2 independent raters, the free-response kappa statistic was 0.820. Aggregation of results within regions of interest resulted in overestimation of agreement beyond chance. The free-response kappa provides an estimate of agreement beyond chance in situations where only positive findings are reported by raters.

Twitter Demographics

The data shown below were collected from the profiles of 2 tweeters who shared this research output. Click here to find out more about how the information was compiled.

Mendeley readers

The data shown below were compiled from readership statistics for 25 Mendeley readers of this research output. Click here to see the associated Mendeley record.

Geographical breakdown

Country Count As %
Unknown 25 100%

Demographic breakdown

Readers by professional status Count As %
Student > Ph. D. Student 6 24%
Researcher 5 20%
Student > Doctoral Student 4 16%
Other 2 8%
Student > Bachelor 2 8%
Other 2 8%
Unknown 4 16%
Readers by discipline Count As %
Medicine and Dentistry 8 32%
Computer Science 2 8%
Biochemistry, Genetics and Molecular Biology 2 8%
Sports and Recreations 1 4%
Social Sciences 1 4%
Other 2 8%
Unknown 9 36%

Attention Score in Context

This research output has an Altmetric Attention Score of 2. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 20 April 2017.
All research outputs
#5,455,223
of 9,716,694 outputs
Outputs from BMC Medical Research Methodology
#643
of 942 outputs
Outputs of similar age
#145,916
of 261,794 outputs
Outputs of similar age from BMC Medical Research Methodology
#21
of 31 outputs
Altmetric has tracked 9,716,694 research outputs across all sources so far. This one is in the 43rd percentile – i.e., 43% of other outputs scored the same or lower than it.
So far Altmetric has tracked 942 research outputs from this source. They typically receive more attention than average, with a mean Attention Score of 7.7. This one is in the 31st percentile – i.e., 31% of its peers scored the same or lower than it.
Older research outputs will score higher simply because they've had more time to accumulate mentions. To account for age we can compare this Altmetric Attention Score to the 261,794 tracked outputs that were published within six weeks on either side of this one in any source. This one is in the 43rd percentile – i.e., 43% of its contemporaries scored the same or lower than it.
We're also able to compare this research output to 31 others from the same source and published within six weeks on either side of this one. This one is in the 32nd percentile – i.e., 32% of its contemporaries scored the same or lower than it.