Research Reports

Application of the M-Index for the LSAT (RR 10-01)

Detection of aberrant test-taker responses is an important component of test security. According to the current research literature, there are five major causes of aberrant responses: answer copying, creative responding, careless responding, lucky guessing, and random responding. From a test security perspective, answer copying is the primary consideration when it comes to paper-and-pencil tests. Answer-copying behavior often results in an unusual agreement between the incorrect answers for a pair of test takers.

A common approach to detecting unusual agreement between the incorrect answers of two test takers is the K-Index probability. The K-Index has been used at the Educational Testing Service (ETS) for decades, and its properties have been further explored in the literature. The major disadvantage of the K-Index is a high Type II (i.e., false-negative) error rate. This paper presents a new approach called the M-Index. A computational study comparing the K-Index with the M-Index demonstrates that the M-Index has a lower Type II error rate and a Type I (i.e., false-positive) error rate below the nominal level.

Request the full report

Additional reports in this collection

researchers study paperwork and examine charts and figures on a tablet

Evidence to Support Validity Claims for Using LSAT Scores...

Law School Admission Test (LSAT) scores provide a standard measure of an applicant’s proficiency in a well-defined set of important skills associated with success in law school coursework. LSAT scores are also a strong predictor of first-year grades (FYG) and cumulative grade point average (CGPA) in law school. The most recent correlational study of LSAT results (2019) shows that LSAT scores are far superior to undergraduate grade point average (UGPA) in predicting FYG...

Understanding and Interpreting Law School Enrollment Data...

The Law School Admission Council (LSAC) has a long-standing commitment to diversity, equity, and inclusion in legal education and in the legal profession. In line with its mission to promote quality, access, and equity in legal education, LSAC is providing this report, Understanding and Interpreting Law School Enrollment Data: A Focus on Race and Ethnicity, to help law schools, admission professionals, and other legal education stakeholders understand how we are measuring who is the pipeline.