Reliability, which is the consistency of test scores or ratings, is one of several ways to assess the quality of a measure. Three major types of reliability, including brief descriptions, are:

• 1.
  Interrater reliability refers to the consistency of the ratings made by two or more observers on the behavior (e.g., classroom behavior) of one or more students.
• 2.
  Internal consistency reliability (e.g., split-half reliability, parallel forms reliability, and coefficient alpha) refers to the degree of uniformity of the item content of a measure. In other words, the degree to which the items on a measure are similar in content to each other. To evaluate the internal consistency reliability, a single administration of the measure is given and then the degree of homogeneity of the item content of the ...