Error in Clinical Research

Lead Author(s): Jeff Martin, MD

Missing the Truth

What are the ways of missing the truth (ie getting the wrong answer)? There are two main ways:

Bias or Systematic Error

Systematic error is also known as bias. Because it is a systematic process, it will cause a distortion from the truth in a predictable (not random) direction. We say that the amount of systematic error is captured in the validity of the inference.

Random Error

In distinction to systematic error, random error occurs because we cannot sample everyone in our studies; Just by chance alone we might draw a sample that is not representative of the source population.

Diagram - Typical Study

When you perform a study you typically just have one shot, as diagrammed below, and you don't know where the center of the target is.


The field of statistics can tell you the random error of your one shot, with definite formulae for confidence intervals, but cannot tell you anything about how close you are to the center.