¿Cómo calcula el GMAT la nota final?

[Etreus]

Muy buenas!

Desde que supe del GMAT me he preguntado cómo hacen los creadores para asignar una nota numérica a los resultados. Tenía muchas teorías acerca del algoritmo que utilizaban, y he buscado bastante por la red. Lo mejor que he encontrado, sin duda, es esta explicación de la página de Manhattan que os dejo aquí:

www.manhattangmat.com/articles/score-calculation.cfm


Es muy recomendable leerla. Pero para el que no quiera o pueda, básicamente dice lo siguiente:

1) Cada pregunta del GMAT tiene una curva o distribución característica de probabilidad acumulada llamada “Item Characteristic Curve”



2) La sucesión de preguntas que nos da el GMAT -y su correspondiente dificultad- depende de dónde nos vayamos encontrando en esta curva con respecto al total de los examinados (datos recogidos durante años).

3) Para cada pregunta hay también asociada una curva inversa, probabilidad acumulada de responder de manera incorrecta (simétrica a la regular, con eje en el 50%).



4) Pues bien, el resultado de cada sección viene dado por la curva o distribución resultante de la siguiente “suma”: por un lado las curvas regulares de las respuestas que hemos contestado correctamente, y por otro las curvas inversas de las respondidas de manera incorrecta. La curva resultante se escala de 0 a 60.

5) Para el valor final de la nota del GMAT toma ambos valores y obtiene un nota final (200-800). Este proceso no lo deja muy claro. Sin embargo yo creo que vuelve a tomar las dos curvas resultantes (una por sección) y en base a ellas calcula una curva final del examen. Esta curva final nos da nuestra nota de GMAT. Ello explicaría por qué para percentiles altos pesa mucho más la parte verbal que la cuantitativa.


Espero que os sirva. Saludos.

Etreus.

[rid]

Gracias Etreus, he añadido un enlace a este post desde la guía del GMAT

[melkart]

Estupenda aportación Etreus!!

Yo sólo quisiera añadir una cosilla al respecto.

El sistema informático del GMAT te va situando en un percentil conforme a lo explicado por Etreus, ahora bien, al principio las oscilaciones en la dificultad de las preguntas son mayores que al final. Me explico, al principio el ordenador no tiene ni idea de en qué percentil situarte, así que te lanza una pregunta de dificultad media, si la haces bien, incrementa mucho la dificultad de la siguiente, si la haces mal te lleva a un nivel entre la primera y la segunda, y así sucesivamente.

El quid de la cuestión está en que conforme vas haciendo preguntas, el sistema más o menos te va ubicando en un percentil y la dificultad de las nuevas preguntas que te lanza es muy semejante a la de la anterior, esto implica que un fallo tonto al principio (cuando la diferencia en la dificultad de las preguntas es mayor) te penaliza mucho, mientras que el mismo fallo hacia el final del examen apenas si tendrá repercusión en tu nota. Por eso merece la pena emplear un poquito más de tiempo en las primeras preguntas aunque luego las últimas las hagas un poco más corriendo y aplicando el famoso proceso de eliminación; ahora bien, tampoco os entretengáis tanto que luego se queden siete u ocho preguntas sin contestar, porque estamos en las mismas.

[rid]

Un artículo relacionado escrito por Veritas Prep en F1GMAT:

How GMAT Scoring Algorithm Works?

The GMAT is a computer-adaptive test where your score is calculated by an algorithm that provides you with harder questions (and higher score returns) when you answer previous questions correctly, and with easier questions (and lower returns) when you’ve answered previous questions incorrectly.

Through this method, the GMAT can determine your ability level in a relatively short period – 37 math and 41 verbal questions – and provide you with an immediate score upon completion of the test. To save you the stress of trying to figure out the secrets of the algorithm, here are some important things you should know about GMAT scoring:


1) Good news: You can get a lot of questions wrong and still do well!

The job of the GMAT scoring algorithm is to determine your ability level by asking you questions that begin to close in on it. Think of how you’d play a game of 20 Questions as you attempt to zero in on the historical figure that your “opponent” has selected:

Was this person famous in the era BC? (No – too early)

Was this person famous before the Middle Ages? (No – still too early)

Was this person famous before the Declaration of Independence? (Yes – 1776 is too late)

Was this person famous before 1600? (Yes – 1600 is still too late)

Did this person become famous before 1500? (Yes – now we’re getting close to that period between around 1300-1500)

Was this person famous in the late 1400s? (Yes – now we’re getting close to really knowing the answer)

Was this person famous for something that happened in the 1490s? (Yes)

Is it Christopher Columbus in 1492? (Yes – once you get to the 1490s, you can be pretty sure that you are talking Columbus. We’ve managed to narrow down our assessment of the figure in question by getting some “yes” and “no” answers)

Essentially, that’s what the GMAT is trying to do with the questions it feeds you. “Is this person above a 700? Yes.” “Is this person above a 750? No.” Because the test needs to get those “no” answers at the upper limit of your ability, it will continue to feed you harder questions that you will likely answer incorrectly as it tests your upper threshold, and at the lower end it will feed you easier questions to test your minimum ability.

The upshot for you? You’re supposed to answer a fair number of questions incorrectly. Everyone does. People scoring in the 46-50 scaled score range on the quant section (the upper limit of high scores) answered between 21 and 26 of the 37 math questions correctly. You can score well above the 90th percentile on math and miss more than a dozen questions!

2) The first ten questions are no more important than the last ten.

The Graduate Management Admissions Council goes as far as to spell this out clearly in the Official Guide for GMAT Review and on its blog, but the rumors still persist. Let’s go back to the game of 20 questions; if it’s that easy for you or I to correctly guess “Christopher Columbus” in just 20 questions, why does the GMAT need 37 or 41 to determine your score? After all, GMAC is run by a sophisticated team of statisticians and psychometricians.

The answer? The GMAT needs to account for false positives and false negatives. In a game of 20 questions, it’s in unbelievably poor form to lie about the answer to a question, but on the GMAT you’ll “lie” about your ability whenever you guess correctly or make a silly mistake and answer incorrectly. The test needs to account for that, and so more questions are needed.

Going back to Columbus, say that the 20 questions proprietor had forgotten that catchy rhyme “In 1492 Columbus sailed the ocean blue”, and tried to estimate your line of time-sensitive questioning by thinking “Jamestown was in the early 1600s, so Columbus must have reached the Americas in the 1500s.” He’d have answered your question “before 1500?” as “no”. But your subsequent questions – “was he an explorer/sponsored by the Spanish crown/etc.” – would eventually bear out that the answer to the pre-1500 question was false.

The GMAT knows that you’ll have some false positives/negatives in your answers, and accordingly it is equipped to filter through those. And, it can’t make any major decisions about your ability level that early in the test. If you’re taking the GMAT soon, hopefully you’re studying probability concepts thoroughly enough to recognize this – 1 out of every 525 test-takers who guesses blindly on the first four questions will get them all right. With well over 200,000 GMATs taken per year, the overseers of the test know that they’ll see quite a few tests that include sets of 3-4 consecutive correct guesses, and the algorithm is set up to mitigate those and accurately reflect your scores.

3) Knowing how the scoring algorithm works neither significantly impacts your score nor excuses you from having to answer questions correctly!

Of the time that most examinees spend preparing for the GMAT, among the least-value-added is the time beyond that first 20 minutes that they spend thinking about the scoring algorithm. Consider this quote from Dr. Eileen Talento-Miller, one of the chief psychometricians behind the GMAT, in her blog post about guessing on the exam:

“And because no one knows what item you would have gotten next if you don’t complete the items at the end, then there is no good way to estimate how that would affect your score.”

If the creators of the exam are willing to admit that they’re unsure how they’d game the test, it’s unlikely that you’ll somehow crack the code on your own. The psychometricians at GMAC are tasked by business schools with, above all else, the job of ensuring that the test is a valid assessment of a student’s performance.

You can spend your time much more effectively by preparing to succeed than by trying to fully understand the nuances of how you’ll be assessed. Ultimately, you should trust that the scoring system will accurately value your performance, and that the only thing you can control is that performance itself.

Artículo original: http://www.f1gmat.com/gmat-scoring-algorithm

[ncp]

Una duda rápida: Entonces por lo que he podido leer aquí; ¿Qué relación tiene en tu nota final del GMAT la parte AWA? Ya que, si no me enterado muy mal, todo el tiempo se habla de la puntuación verbal más cuantitativa....

[melkart]

El AWA puntúa a parte, de 1 a 6. Una nota decente en AWA sería a partir de 4 o 4.5.

[rid]

Añadir que el AWA sirve para muy poco, como dice melkart mientras saques 4.0 o más ya vale. Utilizando estas plantillas http://www.club-mba.com/template-awa/ ya tienes esa nota prácticamente asegurada. Lo verdaderamente importante son las notas de las secciones Verbal y Cuantitativa, que son las que cuentan para la nota sobre 800.

[ncp]

Por cierto, me imagino que no, pero en la parte cuantitativa del GMAT: ¿Se puede usar algún tipo de calculadora??
Gracias!
Sds.

[melkart]

me imagino que no, pero en la parte cuantitativa del GMAT: ¿Se puede usar algún tipo de calculadora??

Imaginas bien :) Las cuentas a papel y boli, así que más te vale recuperar fluidez con el cálculo mental. Yo normalmente planteaba bien los problemas, pero luego llegaba el momento de las operaciones y metía la pata de una manera... :P