Letter to the Editor concerning "Reliability and reproducibility analysis of the AOSpine thoracolumbar spine injury classification system by Chinese spinal surgeons" by J. Cheng et al. (Eur Spine J; 2016: doi:10.1007/s00586-016-4842-4)

The minimum basic dataset for diagnoses of cerebrovascular disease: Methodological issue on reliability

Reliability (precision, repeatability, agreement) and validity (accuracy) are two completely different issues which should be assessed using appropriate tests. It is crucial to know that, reporting concordance rate; the selection error rate and the classification error rate are not the most appropriate estimates to assess reliability. Regarding reliability, for qualitative variables, weighted kappa should be used with caution. However, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio positive and negative as well as diagnostic accuracy are estimates that are usually used to evaluate the validity of a test compared to a gold standard.