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philchalmers / mirt

Multidimensional item response theory
https://philchalmers.github.io/mirt/
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Apply scaling D factor (1.702) to Slope estimates? #199

Closed state-o-flux closed 3 years ago

state-o-flux commented 3 years ago

I'm wondering if it's possible to apply the scaling D factor to alpha parameter estimates in order to estimate the logistic item response model.

philchalmers commented 3 years ago

You can just apply the 1.7 constant after the model has been fitted to each parameter estimate (where applicable). There's really no need to do this in the estimation engine itself.

state-o-flux commented 3 years ago

Thanks, this works but then it won't be applied when running fscores(mirt_model) as the inherited model won't actually have changed. No?

philchalmers commented 3 years ago

The factor score computations would be invariant to a rescaling parameter like D. So even if you included this at the time of estimation the factor scores would be exactly the same under either parameterized scaling.