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Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Systematic error

Systematic (nonrandom) error refers to an error characterized by a consistent pattern to the inaccuracy illustrated¹.

Systematic error is responsible for bias

Example

A target where the scores are closely grouped, but are some distance from the bull’s-eye¹.

There is high precision but low accuracy.

Random Error

Random Error has no consistent pattern to the way in which the scores are dispersed¹

Random error does not cause bias since there is no pattern to the error and tends to be “self-compensating” due to pure probability¹.

Random error causes inference to be difficult by obscuring patterns or relationships of the question the study was designed to answer¹.

Larger sample sizes help to reduce the impact of random errro¹.

References

1.

Sim J, Arnell P. Measurement validity in physical therapy research. Physical Therapy. 1993;73(2):102-110; discussion 110-115. doi:10.1093/ptj/73.2.102