Which approaches are exist for the estimation of a item difficulty from the statistical data?
Are they measure objective item's complexity?
Which approaches are exist for the estimation of a item difficulty from the statistical data?
Are they measure objective item's complexity?
There are three main estimation approaches. For Rasch models estimation can be done using the conditional likelihood approach (used by eRm package in R).
For 2PL or 3PL models you can use marginal likelihood approach (used by ltm package in R).
You can also use MCMC for either models. Any decent introductory textbook should have sections that go over these estimation procedures.