On Wed, 28 Aug 2013 08:31:49 +0100, scott wrote:

>>>> The 700k population of students perhaps doesn't fluctuate much, but
>>>> the difficulty of the questions surely does. But how to control for
>>>> that?
>>>
>>> Isn't that a perfect reason to have a fixed % of people getting each
>>> grade?
>>
>> Depends on whether you need an absolute measurement of skill/knowledge
>> or a relative measurement.
> 
> If the distribution in skill/knowledge of the students is fluctuating
> less than the difficulty of the questions, it will give you a more
> accurate absolute measure (if the alternative is to give everyone grades
> based on the number of questions they get right).
> 
> Given there are only a handful of questions in an exam, and hundreds of
> thousands of students taking them (and hundreds of thousands of
> teachers), I'd say it's way more likely the distribution of question
> difficulty varies from year to year than that of the students' skill.
> 
> Anyway I'd suggest that the main use of school exam grades is to secure
> a place at a college or university, so a relative measure is probably
> all that's needed.

Well, maybe.  If you buy into the idea that pre-uni instruction degrading 
isn't a problem.  An absolute measure can be used to uphold an absolute 
measure, and if the pre-uni schools aren't meeting it, then they need to 
up their game, rather than the universities lowering their standards.

Jim

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