Standard deviation (Edexcel GCSE Statistics): Flashcards
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Practise the cards
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What is the formula for standard deviation in grouped data?
What is the formula for standard deviation in grouped data?
SD = sqrt[(∑fx²/∑f) - (∑fx/∑f)²] for grouped data.
Why do we get estimates instead of exact SD in grouped data?
Why do we get estimates instead of exact SD in grouped data?
Using midpoints to represent all values gives an estimate, not exact.
Which columns must you add for SD calculation?
Which columns must you add for SD calculation?
Midpoint, f×Mid, and f×Mid² columns.
Why is the SD value an estimate?
Why is the SD value an estimate?
Because midpoints approximate all data values within intervals.
How do you round your final SD answer in exams?
How do you round your final SD answer in exams?
To three significant figures unless directed otherwise.
What units are used for the SD in the puzzle time example?
What units are used for the SD in the puzzle time example?
Seconds, matching the original data units.
Find SD from f=40, fT=1820, fT2=104800
Find SD from f=40, fT=1820, fT2=104800
SD ≈ 23.4 s
Calculate f×mid and f×mid² for class 20-40 f=11
Calculate f×mid and f×mid² for class 20-40 f=11
f×mid = 330, f×mid² = 9900
Why is SD from grouped data only an estimate?
Why is SD from grouped data only an estimate?
Midpoints represent class values, not exact data
Calculate SD: ∑f=40, ∑fx=1820, ∑fx²=104800
Calculate SD: ∑f=40, ∑fx=1820, ∑fx²=104800
SD = √(104800/40 - (1820/40)^2) = 23.4 s