[thaumasiotes]

> Typically you have -1/N for incorrect selection, where N is the number of choices. For N=4, you would grade incorrect answers as -0.25.

That is definitely not typical. -0.25 is the appropriate adjustment for N=5. For N=4 you want -0.33. -1/N makes no sense at all.

Note that doing this preserves the expected value of everyone's score, but artificially widens the variation, which you might not want. It does allow you to diagnose partial knowledge, which you probably do want.

[bArray]

Maybe it is typical only for me. I did question it and was told that we don't want to completely remove the incentive for educated guessing. We also usually have a scale of question difficulty, so getting people to a pass is not too difficult if they know the subject at all, but getting towards 100% gets significantly harder.

I think the real reason is that our questions are usually N=4, negative marks of 0.25 allows for quick adding.

[thaumasiotes]

> I did question it and was told that we don't want to completely remove the incentive for educated guessing.

So... you were told some unmotivated nonsense?

On an item with four answers, +1 for a correct answer and -0.25 for a wrong answer means that in expectation you will receive 0.0625 points for a completely uneducated guess. The only correct adjustment you can make is to dock 0.33(3...) for a wrong answer, in which case an uneducated guess is worth 0.0000 points and a minimally-educated guess, one in which you're capable of eliminating just one of the four answers, is worth... 0.0833(3...) points.

> I think the real reason is that our questions are usually N=4, negative marks of 0.25 allows for quick adding.

You think adding fourths is easy, but adding thirds is hard? If you really believe that, it'd be simple enough to add fifth choices to your questions.

Are you sure the real reason isn't just that nobody ever bothered to put any thought into what they were doing?