When IDRA was commissioned to investigate dropout rates in Texas in the mid-1980s, the state had no data at all to work with. IDRA developed a now industry-wide attrition methodology to calculate the number and percent of high school students leaving school prior to graduating with a high school diploma. There are other methods of studying the dropout issue as well, such as dropout rates, graduation rates and longitudinal rates. Though they have different meaning and calculation methods, each provides unique information that is important for assessing schools’ quality of education and school holding power. IDRA’s infographic, 8 Types of Dropout Data Defined, gives an overview of the most-used methods and what they mean.