In other words, it may consistently provide similar results, but it does not measure what the research proposed to determine. This can be tested using the split-half method, whereby the researcher takes the results obtained from one-half of the scale items and checks them against the results of the other half.Īlthough the researcher may be able to prove the research instrument’s repeatability and internal consistency, and therefore reliability, the instrument itself may not be valid. If it is, the instrument shows high consistency. This battery of questions should be answered consistently by the respondent. Probing for attitudes usually requires a series of questions that are similar, but not the same. The problem with the test-retest method is that it may not only sensitize the respondent to the subject matter, and hence influence the responses given, but that we cannot be sure that there were no changes in extraneous influences such as an attitude change that has occurred that could lead to a difference in the responses provided. When different people measure, observe and judge the outcome, there is almost always a variance in the definition of reliability.

A high degree of stability indicates a high degree of reliability, since the results are repeatable. The extent to which different raters or observers react and respond with their prognosis can be one measure of reliability. If we are dealing with a stable measure, then the results should be similar. This attribute of the instrument is actually referred to as stability. The consistency with which questionnaire items are answered can be determined through the test-retest method, whereby a respondent would be asked to answer the same question(s) at two different times. Should you have a question that can be misunderstood, and therefore is answered differently by respondents, you are dealing with low reliability.

In other words, if the results of a study can be reproduced under a similar methodology, then the research instrument is considered to be reliable. The extent to which results are consistent over time and an accurate representation of the total population under study is referred to as reliability.

Definition of reliability in research