org.activemath.studentmodel2.simulation
Class IRT

java.lang.Object
  org.activemath.studentmodel2.simulation.IRT

public class IRT
extends Object

The IRT class implements some aspects of the dichotomous Rasch-Model of the item response theory. Especially, the estimation of a response given the mastery of a simulee (student) and the difficulty of an item. Additionally it's possible to set the discrimination value and a value for guessing. Those values default to no guessing and a discrimination value of 1.117 (according to a Desmarais Paper).

Constructor Summary

IRT()

Method Summary

double	getAnswer(double itemDifficulty, double studentMastery) Get the response of a student with given mastery for an exercise with a given difficulty by using the random function to create a dichotomous response.
double	getCorrectProb(double itemDifficulty, double studentMastery) Calculates the IRT-probability that a student gives a correct answer
double	getCorrectProb(double itemDifficulty, double studentMastery, double discriminationFactor) Calculates the IRT-probability that a student gives a correct answer
double	getDiscriminationVal()
double	getGuessingProb()
static IRT	getInstance() get the IRT singleton
void	setDiscriminationVal(double discriminationVal)
void	setGuessingProb(double guessingProb)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

IRT

public IRT()

Method Detail

getInstance

public static IRT getInstance()

get the IRT singleton

Returns:

- The IRT object

getAnswer

public double getAnswer(double itemDifficulty,
                        double studentMastery)

Get the response of a student with given mastery for an exercise with a given difficulty by using the random function to create a dichotomous response. (either correct (=1) or wrong (=0))

Parameters:

itemDifficulty - - the difficulty of an exercise

studentMastery - - the mastery of the student

Returns:

- The dichotomous achievement for the item (exercise)

getCorrectProb

public double getCorrectProb(double itemDifficulty,
                             double studentMastery)

Calculates the IRT-probability that a student gives a correct answer

Parameters:

itemDifficulty - - difficulty of the exercise (IRT-style) in [0,1]

studentMastery - - mastery of the student in [0,1]

Returns:

- The probability P(Answer = correct) for the item/user

getCorrectProb

public double getCorrectProb(double itemDifficulty,
                             double studentMastery,
                             double discriminationFactor)

Calculates the IRT-probability that a student gives a correct answer

Parameters:

itemDifficulty - - difficulty of the exercise (IRT-style) in [0,1]

studentMastery - - mastery of the student in [0,1]

dicriminationFactor - - the discrimination facor of an exercise

Returns:

- The probability P(Answer = correct) for the item/user

getDiscriminationVal

public double getDiscriminationVal()

Returns:

the discriminationVal

setDiscriminationVal

public void setDiscriminationVal(double discriminationVal)

Parameters:

discriminationVal - the discriminationVal to set

getGuessingProb

public double getGuessingProb()

Returns:

the guessingProb

setGuessingProb

public void setGuessingProb(double guessingProb)

Parameters:

guessingProb - the guessingProb to set