Bias

Synonyms

Participation bias; Selection bias; Systematic bias

Definition

Bias is the difference between the true value of a particular quantity and an estimate of the quantity obtained from scientific investigation. Randomization is a process designed to reduce bias as much as possible.

Description

Various influences can introduce error into the assessment of treatment effects: As an example, here systematic bias is discussed. If all of the subjects in one treatment group share a characteristic that is not present in any of the subjects in the other treatment group(s), it is not possible to ascribe differences between the groups to the influence of central interest in the study, i.e., the different treatments received by the groups. Putting all relatively tall subjects in one group and all relatively short subjects in another group would be an example of systematic bias. Another example would be putting all relatively heavy subjects in one group and all relatively less heavy subjects in...