Reliability indicates the degree to which the measurement instrument is consistent, free from random error, and the measurements of the characteristics of individuals under different conditions yield similar results. There are three ways to analyze reliability: internal consistency reliability, test-retest reliability and inter-rater reliability. Internal consistency reliability is the degree of congruence of items on the questionnaire or scale. Congruence between them suggests that all items measure the same thing as the instrument as a whole. Inter-rater reliability measures the agreement of two or more raters that use the same information on the same analyzing unit. Test-retest reliability is an estimation of the scale of stability over time that is measure of result congruency obtained by repeated measurement on the same objects, under the condition that there was no change in the condition of those objects.