Multiple Choice – To guess or not to guess

Everyone knows that faced with a multiple choice questions with n possible answers a random guess has a 1/n chance of being correct but does anyone pause to consider there is also a (n-1)/n chance of guessing incorrectly and why would that even matter?

CEM who provide some of the 11+ tests are always remarkably reluctant to share any details about what how they process the test results to arrive at the “standardised” marks which are given to parents but there could be some clues gained from looking at the familiarisation booklets published by the schools.  At the time of writing Kendrick school’s website had copies of the advice given to applicants both in 2015 (entry in 2016) and the recent set of tests for entry in 2018.  Two years ago applicants were being told, “candidates will not lose marks for incorrect answers.” but this particular piece advice seems to have quietly disappeared.

A known problem with multiple choice tests is examiners have no control over is the residual variance (‘noise’) introduced by the universal practice of guessing any answers the candidate doesn’t know.  Removing marks for wrong answers doesn’t alleviate this problem it just replaces it with a new source of variance; test takers’ attitude towards risk taking.
Looking further afield the official guidance provided by CEM, published on schools’ websites has changed although it’s not consistent.  Maybe CEM decided that confirming that marks are not removed encourages children to guess, however quietly removing this advice without telling anyone means candidates now need to correctly guess CEM’s strategy for dealing with guessing thus adding more variance to the test.  This hardly seems an objective way to run a test.

So what’s my advice to parents whose children will be sitting the tests next September?  It’s multiple choice – your guess is as good as mine.

Booklets which all say no marks are removed for wrong answers (at the bottom of page 2)

Booklets which make no mention of whether marks are removed or not

If anyone can find any more please leave a comment and I’ll update the list.

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