A systematic bias is sampling error that results from the way in which the research is conducted. It stems from errors in the sampling procedures, and it cannot be reduced or eliminated by increasing the sample size. At best the causes responsible for these errors can be detected and corrected. Usually a systematic bias is the result of one or more of the following factors:
Causes of Systematic Bias
- Inappropriate sampling frame:
If the sampling frame is inappropriate i.e., a biased representation of the universe, it will result in a systematic bias.
- Defective measuring device:
In survey work, systematic bias can result if the questionnaire or the interviewer is biased. Similarly, if the physical measuring device is defective there will be systematic bias in the data collected through such a measuring device.
If we are unable to sample all the individuals initially included in the sample, there may arise a systematic bias. The reason is that in such a situation the likelihood of establishing contact or receiving a response from an individual is often correlated with the measure of what is to be estimated.
- Indeterminacy principle:
Sometimes we find that individuals act differently when kept under observation than what they do when kept in non-observed situations. For instance, if workers are aware that somebody is observing them in course of a work study on the basis of which the average length of time to complete a task will be determined and accordingly the quota will be set for piece work, they generally tend to work slowly in comparison to the speed with which they work if kept unobserved. Thus, the indeterminacy principle may also be a cause of a systematic bias.
- Natural bias in the reporting of data:
There is usually a downward bias in the income data collected by government taxation department, whereas we find an upward bias in the income data collected by some social organization.
People in general understate their incomes if asked about it for tax purposes, but they overstate the same if asked for social status or their affluence. Generally in psychological surveys, people tend to give what they think is the “correct” answer rather than revealing their true feelings.