BMJ  2008;336:789 (12 April), doi:10.1136/bmj.39542.610000.3A

Letters

Predicting citations

Validating prediction models

The first 150 words of the full text of this article appear below.

Lokker et al presented an interesting model to predict citation counts for clinical articles.¹ This topic is so important that the paper will probably attract many citations. We want to clarify some of the nomenclature of validation of prediction models, to avoid confusion in future reporting.

The authors randomly divided 1274 articles into a derivation data set of 757 articles for development of a prediction model and a validation dataset for testing of 504 articles, after exclusion of outliers with >150 citations. This procedure is an example of a split sample approach, but the authors refer to it as cross validation. Cross validation would mean that we develop a model in the first part of the data and test it in the second part, and then repeat the procedure with development in the second part and testing in the first.

The authors report that explained variation (R2) decreased from 0.60 . . . [Full text of this article]

¹ Department of Public Health, Erasmus MC, PO Box 2040, 3000 CA Rotterdam, Netherlands

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Relevant Article

Prediction of citation counts for clinical articles at two years using data available within three weeks of publication: retrospective cohort study

Cynthia Lokker, K Ann McKibbon, R James McKinlay, Nancy L Wilczynski, and R Brian Haynes
BMJ 2008 336: 655-657. [Abstract] [Full Text] [PDF]