The errors are random, so they sometimes have to specified in statistical terms. For a population of parts from the same model number, such as the ADXRS290, the product datasheets typically offer plots that illustrate the bias error distribution or they may offer typical metrics in a specification table, which often reflect one standard deviation of a normal distribution.See Figure 4 and 7, on page 6, of the ADXRS290 datasheet, for example plots:
http://www.analog.com/media/en/technical-documentation/data-sheets/ADXRS290.pdf