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# S3 Edexcel Query watch

1. Hey,So in the Edexcel S3 book, chapter 3 examples 8 and 10, they're using this formula to calculate the estimated variance: (uploaded)

Why is the denominator (n-1) instead of n as usual? Am I missing something completely obvious?

Any help will be much appreciated thanks!
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2. (Original post by Nikhilm)
Hey,So in the Edexcel S3 book, chapter 3 examples 8 and 10, they're using this formula to calculate the estimated variance: (uploaded)

Why is the denominator (n-1) instead of n as usual? Am I missing something completely obvious?

Any help will be much appreciated thanks!
there are 2 different formulas

the one you are quoting is that of an unbiased estimator for the variance of a population, from a sample of n observations and it is denoted by s2
3. (Original post by TeeEm)
there are 2 different formulas

the one you are quoting is that of an unbiased estimator for the variance of a population, from a sample of n observations and it is denoted by s2
Thanks!

is there a proof of as to why it's 'n-1' instead of n?

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4. (Original post by Nikhilm)
Where did they specify that in the book? They didn't quote it in bold as usual?

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Where?
How will I know that ?

5. (Original post by TeeEm)
Where?
How will I know that ?

Lol I realised how stupid that reply was so I edited it but obviously not in time
6. (Original post by Nikhilm)
Lol I realised how stupid that reply was so I edited it but obviously not in time
no worries ... it is late!

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