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S1 Interpolation difficulties

When interpolating for the median for example, do I use exactly n/2 or do I have to round up/go for midpoint between that term and above term?

This is really confusing as it's been different for Solomon/Edexcel papers.
Original post by ColeNate
When interpolating for the median for example, do I use exactly n/2 or do I have to round up/go for midpoint between that term and above term?

This is really confusing as it's been different for Solomon/Edexcel papers.


Use n/2 for edexcel. Ignore any conflicts with Solomon mark schemes, they date back to 2004 and don't necessarily reflect current recommend methods.


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Original post by ColeNate
When interpolating for the median for example, do I use exactly n/2 or do I have to round up/go for midpoint between that term and above term?

This is really confusing as it's been different for Solomon/Edexcel papers.


Use n/2. If the number is a decimal, round up and use that term as the median. If it is an integer, average that term with the term above to get the median.

eg.

1, 3, 5, 6

n/2 = 2. Therefore the median is 0.5(3+5)= 4.

eg2.

1, 3, 5

n/2 = 1.5
Round up to 2nd term. Median is 3
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ColeNate
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Original post by Eux
Use n/2. If the number is a decimal, round up and use that term as the median. If it is an integer, average that term with the term above to get the median.

eg.

1, 3, 5, 6

n/2 = 2. Therefore the median is 0.5(3+5)= 4.

eg2.

1, 3, 5

n/2 = 1.5
Round up to 2nd term. Median is 3


Lots of resources say to do exactly that, but the paper below Q5's mark scheme says otherwise.

https://1a388b28f5ce9318f837a64962fc3ceab9c61da8.googledrive.com/host/0B1ZiqBksUHNYU2s1SVY1VDN2Q0U/June%202014%20(R)%20QP%20-%20S1%20Edexcel.pdf
Original post by ColeNate


Hmm as that is the most recent question and mark scheme similar I'd use that. Surely there is something in the notes section of the MS though
Original post by Eux
Use n/2. If the number is a decimal, round up and use that term as the median. If it is an integer, average that term with the term above to get the median.

eg.

1, 3, 5, 6

n/2 = 2. Therefore the median is 0.5(3+5)= 4.

eg2.

1, 3, 5

n/2 = 1.5
Round up to 2nd term. Median is 3


Original post by ColeNate


You dont use interpolation when you have raw data. Interpolation is used to estimate a median (or quartile etc) of grouped data. If you have grouped data, whether it is discrete or continuous use n/2 and interpolate the exact value it produces.

If you have RAW data use n/2. If this produces in integer value take the midpoint of that term and the one above. If it is a decinmal value round up to the next term in the ordered list.

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