Psychological testing is the branch of psychology in which we use standardized tests, construct them in order to understand the individual differences. Development of good psychological test requires thoughtful and sound application of established principles of test construction.
According to Martinez, M. (2015, March 03), one of the stages is Reliability of final test. There are 2 types of reliability, Internal and external . Internal reliability assesses the consistency of results across items within a test. External reliability refers to the extent to which a measure varies from one use to another. In this stage random and systematic errors are checked for. Random error exists in every measurement and is often major source of uncertainty. Systematic error is caused due to instruments, machines, and measuring tools. It is not due to individuals. Systematic error is acceptable we can fix and handled it.
To check reliability the methods used are, test retest, alternate form and split-half method. Test-retest method is the commonly used methods of testing reliability. The test retest method assesses the external consistency of a test. Examples of appropriate tests include questionnaires and psycho metric tests. It measures the stability of a test over time. In alternate form two equivalent forms of the test are administered to the same group of examinees. An individual has given one form of the test and after a period of time the person is given a different version of the same test. The split half method assesses the internal consistency of a test. It measures the extent to which all parts of the test contribute equally to what is being measured. The test is technically spitted into odd and even form.