Contents
What is the cause of measurement error?
Sources of systematic errors may be imperfect calibration of measurement instruments, changes in the environment which interfere with the measurement process, and imperfect methods of observation. A systematic error makes the measured value always smaller or larger than the true value, but not both.
What are the effect of systematic error?
Systematic errors will shift measurements from their true value by the same amount or fraction and in the same direction all the time. These do not affect the reliability (since they’re always the same) but affect accuracy. These usually arise from problematic or incorrectly used equipment, e.g. poor calibration.
When does measurement error inflate the correlation coefficient?
If we select subjects to give a wide range of the measurement, the natural approach when investigating measurement error, this will inflate the correlation coefficient. The correlation coefficient between repeated measurements is often called the reliability of the measurement method.
What happens when you have a measurement error in Y?
Random measurement error in Y does not cause the slope coefficient to be biased – but it does cause the standard error for the slope coefficient to be larger and the t value smaller. Again we run the true regression followed by the regression of Y with Xt.
How is the correlation coefficient used in psychology?
The correlation coefficient between repeated measurements is often called the reliability of the measurement method. It is widely used in the validation of psychological measures such as scales of anxiety and depression, where it is known as the test-retest reliability.
How are pairs of measurements used to investigate measurement error?
A common design for the investigation of measurement error is to take pairs of measurements on a group of subjects, as in table 1. When we have pairs of observations it is natural to plot one measurement against the other.