Question

What is meant by trait level and item difficulty in IRT (Item Response Theory)?

Provide an example with two items to illustrate. If an item has a difficulty level of 2.0,

then what is trait level for someone who has a .50/.50 probability of getting it correct?

Answer 1

ANS.Item response theory(IRT)--It was the theory developed in 1970 for the Scholastic aptitute test (SAT). The estimation is based on a set of parameter values for predicting the desired results. It has broader analysis potential than the standard classical testing exams used earlier for testing the student potential. The classical testing is based on the standard error calculation,mean,median and mode calculation. 2-parameter logic model Mplus software model is used for analyzing the values of depression in patients on a predetermined scale.CES-D, region for epidemiological studies model scale to access the levels of depression in a particular situation and to analyze the validity of a perticular question in an antidepression survey conducted by a group of volunteers. It is a given a scale of 2(moderate periods of time for 2-3 days). The IRT curve is monotonic with an S-shaped curve depicted in the diagram plotted in the given particular situation.There are various parameters of theta which has value ranging from -6 to value of +6.The theta value of zero indicates an 50% probability or 0.50 probability of occurence of the event. The item discriminator parameter value is predicted by the slope parameter.3-IRT model is used for the analysis of item difficulty,3-item lack of positive scale,D factor rule,parameter guessing and lack of positive effect and attitude in life.1-parameter logic rule or Rasch rule depicts the item discrimination model.