What are the main evaluation methods of scale reliability?

There are four methods to evaluate the reliability of the scale, namely, retest reliability, repetition reliability, internal consistency reliability and rater reliability.

Reliability is based on true score theory, but in actual measurement, due to the existence of errors, it is difficult to obtain the true score, so we generally use statistical methods to obtain the reliability of the test by calculating the correlation coefficient.

Relationship between validity and reliability

The relationship between validity and reliability can be understood by the formula O=T+S+R of the measured value. If the measurement is completely valid, that is, 0=T, S=0, R=0, then the measurement at this time must be completely reliable. If the reliability of the scale is insufficient, it will not be completely effective because there is O = T+R.

If the scale is completely credible, it can be completely effective or not, because there may be errors. Although lack of reliability is bound to lack validity, reliability cannot reflect validity.

Reliability is a necessary but not sufficient condition for validity. Theoretically, quantity should have sufficient validity and reliability; From a practical point of view, a good scale should also be practical. Practicality refers to the economy, convenience and interpretability of the scale.