A good research instrument is reliable and usable. Reliability means the instrument consistently measures what it is intended to measure and yields the same results over time. There are several methods to measure reliability, including test-retest, parallel forms, split-half, and internal consistency. Usability means the instrument can be easily used by researchers and educators without expending excessive time, money, or effort. Factors that determine usability include how easy the instrument is to administer, score, interpret, and its cost and format.