Estimation of coefficients of individual agreement (CIAs) for quantitative and binary data using SAS and R

The coefficients of individual agreement (CIAs), which are based on the ratio of the intra- and inter-observer disagreement, provide a general approach for evaluating agreement between two fixed methods of measurements or human observers. In this paper, programs in both SAS and R are presented for estimation of the CIAs between two observers with quantitative or binary measurements. A detailed illustration of the computations, macro variable definitions, input and output for the SAS and R programs are also included in the text. The programs provide estimations of CIAs, their standard errors as well as confidence intervals, for the cases with or without a reference method. Data from a carotid stenosis screening study is used as an example of quantitative measurements. Data from a study involving the evaluation of mammograms by ten radiologists is used to illustrate a binary data example.