In Lesson 20, we said that measures that are free of random errors are said to be reliable. Reliability is the degree to which a measuring instrument or tool is consistent or demonstrates consistency on repeat trials.

There are two main methods of estimating reliability;

• Repeated measurements and
• Internal consistency. 

In this lesson, we shall discuss repeated measurements method.

Repeated measurement method means that reliability is determined by administering an instrument to the respondent, take the score then after some time administer the same instrument to the same respondents and take the second score. Then correlate the two scores to obtain correlation coefficient value which is the reliability coefficient value.

There are three methods of determining reliability under repeated measurement method. This is test-retest, Alternative forms and Equivalent forms method. All these three are discussed in this lesson.