by user3233712
Last Updated April 19, 2018 14:19 PM

I am estimating `standard error`

for `IRT-2PL`

and `IRT-3PL`

models. For `IRT-2PL`

, some of the standard errors are equal to `NA`

while in IRT-3PL **all** standard errors are equal to `NA`

. To clarify more, I have around 30 items, which the standard error for 28 of them is correct while the standard error for two of them is NA (this is for IRT-2PL). In IRT-3PL, the standard error for all 30 items is equal to `NA`

.

What would be the reason for getting these NA?

Here is some statistic about the data:

Number of users: 144

Number of items:30

Number of total user-item transaction =2646

Data sparsity:40.7%

user-item response is binary (0 or 1), i.e. if a user could answer a question (item) correctly, the value is 1 otherwize 0.

FYI, I am using the `ltm`

package in `R`

to estimate the standard error.

Appreciate!

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