Fig. 1.

Random error and systematic error. The black center represents the “truth”. The individual dots represent the results of studies. (A) The dots do not fall on the black center is because of a small degree of random error. (B) The dots are more widely dispersed because of a larger degree of random error. (C, D) The dots or results of individual studies are off target because of systematic error. In (C) there is a small degree of random error, while (D) shows a larger degree of random error (from Gary Gronseth, MD, with permission)