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Future JD Students

LSAT Scores as Predictors of Law School Performance

Over the years, the vast majority of law schools have participated in LSAT validity studies that examine the relationship between students’ LSAT scores and their first-year grades in law school. The studies show that LSAT scores help to predict which students will do well in law school. Moreover, a combination of students’ scores and undergraduate grade-point averages (GPAs) gives a better prediction than either the LSAT or the GPA alone.

Correlation is stated as a coefficient for which 1.00 indicates an exact positive correspondence between candidates’ test scores and subsequent law school performance. A coefficient of zero would indicate nothing more than a coincidental relationship between test scores and subsequent performance. The closer to 1.00 the correlation coefficient is, the greater the test’s predictive validity. In other words, the closer to 1.00 the correlation coefficient is, the less chance there will be of candidates with high LSAT scores failing in their studies or candidates with low test scores performing at the top of their law school class.

The correlation between LSAT scores and first-year law school grades varies from one law school to another (as does the correlation between GPA and first-year law school grades). During 2014, validity studies were conducted for 178 law schools. Correlations between LSAT scores and first-year law school grades ranged from .19 to .56 (median is .38). The correlations between UGPA and first-year law school grades ranged from .06 to .43 (median is .26). However, correlations between LSAT scores combined with undergraduate grade-point averages and first-year law school grades ranged from .31 to .64 (median is .48).

The LSAT, like any admission test, is not a perfect predictor of law school performance. The predictive power of an admission test is limited by many factors, such as the complexity of the skills the test is designed to measure and the unmeasurable factors that can affect students’ performances (e.g., motivation, physical and mental health, or work and family responsibilities). The LSAT is a strong predictor of first-year law school grades and compares very favorably with admission tests used in other graduate and professional fields of study.

Test Score Accuracy—Reliability and Standard Error of Measurement

Reliability is a measure of how consistently a test measures the skills being assessed. The higher the reliability coefficient for a test, the more certain we can be that test takers would get very similar scores if they took the test again.

LSAC reports an internal consistency measure of reliability for every test form. Reliability can vary from 0.00 to 1.00, and a test with no measurement error would have a reliability coefficient of 1.00 (never attained in practice). Reliability coefficients for past LSAT forms have ranged from .90 to .95, indicating a high degree of consistency for these tests. LSAC expects the reliability of the LSAT to continue to fall within the same range.

LSAC also reports the amount of measurement error associated with each test form, a concept known as the standard error of measurement (SEM). The SEM, which is usually about 2.6 points, indicates how close a test taker’s observed score is likely to be to his or her true score. True scores are theoretical scores that would be obtained from perfectly reliable tests with no measurement error—scores never known in practice.

Score bands, or ranges of scores that contain a test taker’s true score a certain percentage of the time, can be derived using the SEM. LSAT score bands are constructed by adding and subtracting the (rounded) SEM to and from an actual LSAT score (e.g., the LSAT score, plus or minus 3 points). Scores near 120 or 180 have asymmetrical bands. Score bands constructed in this manner will contain an individual’s true score approximately 68 percent of the time.

Measurement error also must be taken into account when comparing the LSAT scores of two test takers. It is likely that small differences in scores are due to measurement error rather than to meaningful differences in ability. The standard error of score differences provides some guidance as to the importance of differences between two scores. The standard error of score differences is approximately 1.4 times larger than the standard error of measurement for the individual scores.

Thus, a test score should be regarded as a useful but approximate measure of a test taker’s abilities as measured by the test, not as an exact determination of his or her abilities. LSAC encourages law schools to examine the range of scores within the interval that probably contains the test taker’s true score (e.g., the test taker’s score band) rather than solely interpret the reported score alone.

Adjustments for Variation in Test Difficulty

All test forms of the LSAT reported on the same score scale are designed to measure the same abilities, but one test form may be slightly easier or more difficult than another. The scores from different test forms are made comparable through a statistical procedure known as equating. As a result of equating, a given scaled score earned on different test forms reflects the same level of ability.

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