Reliability
Internal reliability
This is a measure of the extent to which something is consistent within itself.
E.g. All the questions on a IQ test should be measuring the same thing.
However internal consistency isn't always important, say for example, a questionnaire about day-care experiences might look at many different aspects of day care and its effects.
External reliability
This is a measure of consistency over several different occasions.
E.g. If an interviewer conducted an interview, and then conducted the same interview with the same interviewee a week later, the outcome should be the same - otherwise the interview is not reliable.
Reliability also concerns wheather two interviewers produce the same outcomes, this is called inter-interviewer reliability.

Assessing reliability:
Internal reliability - Split-half method
A single group of participants all take a test once. Their answers are then divided in half. This could be done using odd or even numbers or just half the questions.
The individual's scores on both halves should be very similar. The two scores can be compared by calculating a correlation coefficient
External reliability - Test re-test method
A group of participants are given a test or questionnaire or interview once and then again sometime later. The answers can be compared and should be the same. If the tests produce scores, these can be compared by calculating a correlation coefficient.

Improving Reliability
-Removing those items which are most inconsistent. The only way to do this is by trial and error - remove one item and see if the spilt-half correlation coefficient improves. If it does, then the removed item should be permanently left out.

	Created by Lily Gray almost 11 years ago

A-Level Psychology Note on Self-Report Techniques - Validity, Reliability and Ethical Issues, created by Lily Gray on 05/12/2013.