[IPAC-List] Angoff method of setting pass points - how many minimally competent candidates pass at a given pass point?

[Shekerjian, Rene]

I am trying to understand how the Angoff method of setting passpoints affects passing rates. I am not sure if my reasoning is correct, and I was hoping for to get some help from this august body.

Roughly, my understanding is that the Angoff method has SMEs indicate the probability that a minimally competent person would get each item correct. SMEs' item-probability ratings are averaged, and the averages are summed across the items in the test to arrive at the passpoint.

Suppose that for all items in a ten-item test, the average rating is .5 This would mean that a minimally competent candidate would have a 50% chance of getting each item right. If this is true, and all 10 items are perfectly inter-correlated, then half the minimally competent candidates should have a score of 0 and half of them should have a score of 10. As the item intercorrelations decrease, the scores distribution (of minimally competent candidates) should have more candidates at scores in between 0 and 10. 

It seems to me that if you set the pass point at 5 in this example, which the Angoff method would lead you to do, typically about half the minimally competent candidate would pass and about half would fail. 

Is that considered acceptable? Or are we obligated to pass all minimally competent candidates? Or at least avoid knowingly failing minimally competent candidates?

I will appreciate any help anyone offers.

Thanks, 
René