6
votes
1answer
91 views

Item reliability or fit in IRT-based adaptive tests?

My background is in machine learning and statistics, but I am relatively new to psychometrics and testing. Nearly all of the literature I've found on item reliability refers to Chronbach's alpha or ...
1
vote
1answer
84 views

Using Ltm package to calclate 3PL some lines of data seem to go missing

I am hoping someone can help with the following: I have been trying to use the ltm package in R to get person fit estimates using a 3PL model. The problem I have been having is that I start off ...
3
votes
1answer
168 views

Item response theory vs. summative Likert scale

If the items to be "summed" or combined to create an overall index are collectively the underlying construct (i.e. I am trying to measure compliance to an intervention which has different ...
2
votes
1answer
271 views

IQ adaptive test items in 1pl, 2pl or 3pl IRT model?

Some adapative test systems (e.g. school assessment tools) use the 1pl IRT model, while others use the 2pl or the 3pl. When developing an adaptive IQ test, is there a rule of thumb about which model ...
1
vote
1answer
158 views

How to select next item in polytomous CAT / MIRT?

To make a Computerized Adaptive Test out of a sample of 20 dichotomous items a typical course of action would be to: 1) calibrate respondent data with a R package like mirt or ltm using Rasch, 2PL ...
5
votes
1answer
135 views

IRT/Rasch modeling with very large N

I want to fit a 1-parameter IRT model on a questionaire with 15 questions and about six million people. Considering the large N, standard errors aren't essential. It looks like the IRT world is sort ...
5
votes
1answer
749 views

IRT in R: Does anyone know of an IRT item calibration function that can cope with NA's?

I have a dataset that looks like this. ...
0
votes
2answers
825 views

Error message from grm() in ltm: subscript out of bounds

I am analyzing a survey data set. One of the items in the survey is: ...
2
votes
1answer
172 views

Item information in IRT with item covariates (linear logistic test model)

Short question: How does the calculation and interpretation of IRT item information and test information change in the presence of item properties? Long question: There's a variation on IRT called ...
3
votes
1answer
146 views

Item information in IRT

According to item information curves, item information for a 2PL IRT model is $I(\theta)=a^2_i p_i(\theta) q_i(\theta)$ To determine $p_i(\theta)$ and $q_i(\theta)$, do you just use the observed ...
4
votes
1answer
518 views

Internal consistency reliability in item response theory models

How can internal consistency reliability of a test and of individual test items be quantified in Item Response Theory models? I know I can resort to Classical Test Theory, Cronbach's alpha, and other ...
2
votes
0answers
121 views

Testing graded response model thresholds for significance?

I have a data set in which two raters have each rated N samples using a 5-point ordinal rating scale. My primary interest is in whether these two raters make significantly different use of those ...
4
votes
3answers
241 views

Are discrimination parameters in two-parameter IRT models only specific to items?

Discrimination parameters in two-parameter model from IRT are usually considered item parameters. But I've come to doubt it. Think about psychophysics; for example, detecting luminance. I don't ...
3
votes
0answers
300 views

Dealing with poor fit in an Item Response Theory model

I'm studying an online course with about 3000 students who each took several quizzes and I'm trying to apply Item Response Theory (using the ltm package in R) to model the questions, determine which ...
14
votes
4answers
5k views

How to get started with applying item response theory and what software to use?

Context I have been reading about item response theory, and I find it fascinating. I believe I understand the basics, but I am left wondering how to apply statistical techniques related to the area. ...
1
vote
3answers
921 views

Is there an R package which implements weighted maximum likelihood for Rasch models?

Is there a package in R which implements the weighted maximum likelihood method (Warm, 1996) for estimating the person parameters in Rasch Models?