Some Problems With the Analytical Argument in Support of RP67 in the Context of the Bookmark Standard Setting Method

The choice of response probability in the bookmark method has been shown to affect outcomes in important ways. These findings have implications for the validity of the bookmark method because panelists' inability to internally adjust when given different response probabilities suggests that they are not performing the intended judgment task. In response to the concerns these findings raise, proponents of the bookmark method argue that such concerns can be addressed by using a response probability of .67. A crucial part of their argument includes the often-repeated claim that the .67 value corresponds with the maximum information for a correct response, which is believed to be beneficial in some way. In this article, it is shown that this claim is mistaken; that the formula upon which the .67 result is based is incorrect; that (for the relevant measurement model) there is no difference between the information for a correct response, for an incorrect response, or for the item overall; and, more generally, that the "maximize information" approach is based on the wrong likelihood function altogether.