In quantitative research, reliability measures an instruments stability and consistency. In simpler terms, reliability is how well an instrument is able to measure something repeatedly. There are several factors that can influence reliability. Some of the factors include unclear questions/statements, poor test administration procedures, and even the participants in the study.

In this post, we will look at different ways that a researcher can assess the reliability of an instrument. In particular, we will look at the following ways of measuring reliability…

• Test-retest reliability
• Alternative forms reliability
• Kuder-Richardson Split Half Test
• Coefficient Alpha

Test-Retest Reliability

Test-retest reliability assesses the reliability of an instrument by comparing results from several samples over time. A researcher will administer the instrument at two different times to the same participants. The researcher then analyzes the data and looks for a correlation between the results of the two different administrations of the instrument. in general, a correlation above about 0.6 is considered evidence of reasonable reliability of an instrument.

One major drawback of this approach is that often given the same instrument to the same people a second time influences the results of the second administration. It is important that a researcher is aware of this as it indicates that test-retest reliability is not foolproof.

Alternative Forms Reliability 

Alternative forms reliability involves the use of two different instruments that measure the same thing. The two different instruments are given to the same sample. The data from the two instruments are analyzed by calculating the correlation between them. Again, a correlation around 0.6 or higher is considered as an indication of reliability.

The major problem with this is that it is difficult to find two instruments that really measure the same thing. Often scales may claim to measure the same concept but they may both have different operational definitions of the concept.

Kuder-Richardson Split Half Test

The Kuder-Richardson test involves the reliability of categorical variables. In this approach, an instrument is cut in half and the correlation is found between the two halves of the instrument. This approach looks at internal consistency of the items of an instrument.

Coefficient Alpha

Another approach that looks at internal consistency is the Coefficient Alpha. This approach involves administering an instrument and analyze the Cronbach Alpha. Most statistical programs can calculate this number. Normally, scores above 0.7 indicate adequate reliability. The coefficient alpha can only be used for continuous variables like Lickert scales

Conclusion

Assessing reliability is important when conducting research. The approaches discussed here are among the most common. Which approach is best depends on the circumstances of the study that is being conducted.