# how accurate should a percentage be?

Discussion in 'Mathematics' started by Karvol, Nov 14, 2011.

1. ### KarvolOccasional commenter

To a certain extent it is the schools choice and I don't think that there is a right or wrong answer.
I would say, though, that anything above 1 decimal place is slightly ridiculous unless you have numbers where this makes sense.
My school doesn't publish its results ( although we are not in the UK ) and those for internal usage are to 1 d.p.

2. ### Kez101

They can use what they want but, to be honest, the % data isn't really the best measure where there are 19 students. It gets even worse the less there are. So, if one student passed (out of a cohort of 1) there would be 100% - looks great except really it's covering up a multitude of reasons why you shouldn't use it for predictions! Obviously, say, Maths with a cohort of 100 or more, then % get more sensible. A reasonable degree of accuracy would be no decimal places, but I suppose they can choose two if they want.

3. ### frustumStar commenter

One year, the KS2 results for a school near here showed the percentage of children getting L4+ in the tests to be 12 percentage points below the teacher assessment. Made it look like the year 6 teacher was giving them much higher levels than she should. Actually, the difference was the three children who missed L4 by one mark in the test.

When we have the annual "the percentage getting level 4 and above has risen by..." story, I can't help thinking that a lot of it boils down to rounding. 100 marks in the test, and we can presumably assume that there's a roughly normal distribution. So (without doing any actual calculation), I would guess that there's probably at least 2% of the cohort on each of the marks around the level 4 borderline. So either there's going to be an increase, or a fall. I wouldn't be surprised if politics enters the decision as to which it will be...