Monday, February 28, 2011

Understand your LSAT Raw Score to Scale Score Conversion

The February 2011 LSAT scores should be emailed sometime this week, so we hope that you end up with the score you wanted! For everyone else, you can still benefit from the graphs we've got showing how the raw score translates into the 120-180 scale score, and what people mean when they ask "Was it a hard or easy curve?" At Zen of 180, we advocate calling it a generous or ungenerous curve.

All LSATs are normed against the previous so that, statistically speaking, a person who got a 172 on the December 2007 should score within a specified band, +/- 2 of the reported score. This is to normalize performance across LSATs that obviously have different questions: so, that the person might miss 8 questions on one LSAT and 12 on another, but still earn the same scale score of 172. 

The first PrepTest (-8) would be a hard curve, and the second PrepTest (-12) would be a easy curve. Here's where it gets confusing: the latter test would have, on average, harder questions, making the same person miss more and still be performing at the same (scale score) level.

So, at Zen of 180, we refer to these scales as generous or ungenerous. A generous curve makes up for harder questions, while an ungenerous curve compensates for easier questions. The concepts are the same, but the language makes it more clear what the relationship is between the number of questions you can miss and your eventual scale score.

For you visual learners, here's a graph comparing the average and range fluctuations of PrepTests from 52-61 with the actual range of PrepTest 62.

PT 62 has a generous curve, and thus harder questions: the higher the curve, the more questions than you could miss and still get the same scale score.
In the graph, the gray vertical lines for each scale score show the range of raw scores that produced that result in PrepTest 52-61. For example, the lowest raw score for 173 was 7 missed questions, and the highest was 10. 

PrepTest 62 was beyond that highest range at 11 missed questions--making it a generous curve--and it was 3 missed questions more than the middle quartiles, which are shown by the darker horizontal bands cutting across the range lines.

Hopefully this makes it clear why you can take a PrepTest, miss four more questions than you're used to, and yet still get the same scale score. Worse yet is when you miss four fewer questions, and you still get the same scale score and feel like you were tricked by LSAC! Keep in mind that the scores are normalized across all PrepTests, so be sure to compare your scale scores to each other rather than just your missed questions.

Below is the complete graph for PrepTest 62, from 180-120, as well as a graph linking to an explanation of the scale score's interaction with the bell curve.
PrepTest 62's is a "generous" curve. Click for larger view.