What you need to know about statistics Part I: validity of diagnostic and screening tests.

The intent of this manuscript is to provide guidance and support to clinicians and investigators for reporting the results of screening and diagnostic tests. This article is the first of two parts addressing statistics in imaging research. In this part validity measures are discussed. In part II reliability measures will be discussed. In discussing validity, the following concepts will be introduced: (1) functions of diagnostic tests, (2) statistical characteristics of diagnostic tests and application of validity measures, (3) power and sample size for testing the sensitivity and specificity of the diagnostic test, (4) statistical versus clinical significance and (5) characteristics of a useful diagnostic test.