estimation lesson 3 aims:
DESCRIPTION
Assumptions or Theory for Summary table of which CI formula to use Parent Distribution Variance Assumptions or Theory for C I Normal X~(µ,σ2) Known Not normal Unknown Unknown Note: If sample is < 30 and not from a normal distribution we can’t use either the z or t distribution to model the situationTRANSCRIPT
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Aims:• To be able to decide which distribution to use when constructing a C.I. • To practice exam style questions.• To be able to calculate the unbiased estimates for the mean and variance.
Estimation Lesson 3
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ParentDistribution
Variance Assumptions or Theory for
C I
NormalX~(µ,σ2)
Known
Not normal Known
Not normal
NormalX~(µ,σ2)
n
zxn
zx ,
nszx
nszx ,
1 1,n ns sx t x tn n
2__2
2
1x
nx
nns
X
n
zxn
zx ,
Unknown
2__2
2
1x
nx
nns
Unknown
Summary table of which CI formula to use
2~ ,
no CLT
n
X N n
2
30
~ ,
CLT yes
n
X N n
2
30
~ ,
CLT yes
n
sX N n
2
30
~ ,
CLT no
n
sX T n
Note: If sample is < 30 and not from a normal distribution we can’t use either the z or t distribution to model the situation
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Unbiased Estimates of the Mean & Variance
The variance if unknown can be calculated by using the formula below and we call it s2 rather than σ2
2
222 1 s1 1
xn x x xn n n
The unbiased estimate of the mean from a sample is calculated using:
nx
x
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Jan 08 Exam Questionof Nadal’s
of Nadal’s
on Nadal’s
6 mins have a go!
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1. Complete relay race2. Do revision Exercise page
107. Qu 1 to 5 compulsory, 5 to 9 optional
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