What is: 1. Difficulty 2. Sensitivity of an item

1. Difficulty - Pi = ni (how many correct answers you received – per 1 item) / N (in a group of Ss – N = all Ss) 2. Sensitivity - d = p’i – p”I (difference of 2 powers = the lvl of difficulty which you measured among the Ss with better scores or in the 1st half of the Ss who scored best and then you find the power in a group of the 2nd half of the Ss – the difference tells you the sensitivity)