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Christian Lawson-Perfect2 years, 1 month ago

Gave some feedback: Ready to use

Christian Lawson-Perfect2 years, 1 month ago

Saved a checkpoint:

Looks good!

Published this.

Elliott Fletcher2 years, 2 months ago

I have awarded part b) with a mark and tried to use careful wording in parts b) and c).

Elliott Fletcher2 years, 2 months ago

Gave some feedback: Needs to be tested

Elliott Fletcher2 years, 2 months ago

Gave some feedback: Has some problems

Chris Graham2 years, 2 months ago

Gave some feedback: Has some problems

Chris Graham2 years, 2 months ago

I do like this question, however as it stands the marking is unsatisfactory. If there are no marks for b) then it is very hard to justify the mark for c), since it depends directly on the student's interpretation. I would prefer Christian's suggestion below of careful wording and keep the mark in part b). You need the same careful wording in c) too.

Elliott Fletcher2 years, 2 months ago

Thanks for your feedback Christian, i have changed part a to a "what's your opinion" question and awarded it no marks. Also i have added an extra part before this question asking the student to calculate the experimental probabilities of tossing heads for coin 1 and coin 2.

Elliott Fletcher2 years, 2 months ago

Gave some feedback: Needs to be tested

Christian Lawson-Perfect2 years, 2 months ago

Gave some feedback: Has some problems

Christian Lawson-Perfect2 years, 2 months ago

Saved a checkpoint:

I just don't know if there should be any marks for part a! If it was just a "what's your opinion" question, with no marks, then part b might challenge the student's intuition if they picked coin 2.

Working out experimental probabilities for the two coins as a first step might help - P(heads) would be higher for coin 2, but the point is that the sample size is small.

Or, the wording needs to be much more careful. Something like, "for which coin is there more evidence of bias?"

Elliott Fletcher2 years, 2 months ago

Gave some feedback: Needs to be tested

Chris Graham2 years, 2 months ago

Gave some feedback: Has some problems

Chris Graham2 years, 2 months ago

I got 5 heads and 5 tails for the "distractor", which makes part a) very straightforward. I suggest that the imbalance in proportion of heads/tails is greater for coin 2 that coin 1, as it was when you put it up on the screen in the learning lab.

I suggest the following changes to the wording:

• In the statement on the first line: "It is known that one of the coins is biased".
• Part a): "Based on the available results, ..."

• "..., which would be the case for an unbiased coin". It is true in any case. The point being for an unbiased coin you would expect this to approach 0.5. You should explicitly state this.
• "theoretical probability... should be..." it is a fact for an unbiased coin, no should about it.
• "is greater than 50%" would cover 70, 51, 50.00001. You probably don't want to get bogged down in compound probability calculations, but "signficantly different" would be an improvement.
• Same with the "is greater than 50%" in part b).

Elliott Fletcher2 years, 2 months ago

Gave some feedback: Needs to be tested

Elliott Fletcher2 years, 2 months ago

Created this.
Which coin is more likely to be biased? Ready to use Elliott Fletcher 01/08/2017 13:23
Which coin is more likely to be biased? draft Xiaodan Leng 11/07/2019 01:59

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