1. In a Rasch model (1PL) what effect does increasing an item difficulty parameter (b) have on the item characteristic curve (ICC)? Explain with a concrete example.

Answer question using the requirements below. Please use a unique example (i.e., do not reference specific examples used by others).

1. In a Rasch model (1PL) what effect does increasing an item difficulty parameter (b) have on the item characteristic curve (ICC)? Explain with a concrete example.

In you example, include a brief description of

• the latent trait the item represents,
• the scale of the latent trait axis for the ICC (i.e., range of θ),
• example values for the lower and higher difficulty levels (i.e., low and high b index), and
• example values of the probability of getting the item correct at different levels of the trait for the two levels of item difficulty (i.e., illustrate with your description and specific values how the probability of getting the item correct changes at specific trait levels for the different levels of item difficulty).

Hint: Use the attached excel spreadsheet to help you (i.e., change the b index and see how the curve changes).