Item keying

[Hynek Cígler]

Dear Phil,
I suggest a minor and not-so-important improvement to several mirt functions regarding item keying.

In many cases, reverse-keyed items are present in the data. They do not need to be reverted before analysis in mirt, which results in negative discrimination parameters. I actually prefer this option in most cases.
However, in some situations, initial item reversals is necessary – for example, when plotting test information or total test score functions, or when estimating EAPsum factor scores (or reliability). This limitation is quite inconvenient.

The implementation should be fairly straightforward: a new parameter, such as key = c(1, 1, -1, -1, …), could be introduced.

I also suppose that item_weights parameter in fscores function could be used, but I am not sure and this doesn't help in plotting functions.

Thank you for the consideration!

Best Regards,
Hynek