my presentation01
TRANSCRIPT
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GROUP PRESENTATIONGROUP PRESENTATIONSAMPLE SIZE DETERMINATION
:-INSTRUCTOR SIR FARHAN AHMED
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GROUP PRESENTATIONGROUP MEMBERS
Faizan AhmedAhsan Alvi
Muneeb Ahmed
Fahad Amin
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TOPICS TO BE
DISCUSS1.Determining sample size.
2.Sampling error.
3.Determining sample size if is unknown.4.Discuss Ethical Issues.
5.Determining sample size on the basis ofjudgment.
6.
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Determining Sample
Size
For theMean
DeterminingSample Size
For theProportion
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Determining SampleSize
For theMean
DeterminingSample Size
nZX
nZe =
Sampling error( )margin of error
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Determining SampleSize
For theMean
DeterminingSample Size
n
Ze =
( )continued
2
22
e
Zn =
Now solve forn to get
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Sampling ErrorThe required sample size needed to estimate apopulation parameter to within a selectedmargin of error (e) using a specified level of
confidence (1 -
) can be computed
The margin of error is also called samplingerror
the amount of imprecision in the estimate of
the population parameterthe amount added and subtracted to the
point estimate to form the confidenceinterval
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Determining Sample
SizeTo determine the required sample size forthe mean, you must know:
The desired level of confidence (1 - ),
which determines the critical Z valueThe acceptable sampling error, e
The standard deviation,
( )continued
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Required Sample SizeExample
If = 45, what sample size is needed to
estimate the mean within 5 with 90%
confidence?
( )Always round up
219.195
(45)(1.645)
e
Zn
2
22
2
22
===
So the required sample size is n= 220
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If is unknownIf unknown, can be estimatedwhen using the required sample
size formulaUse a value for that is expected
to be at least as large as the true
Select a pilot sample and estimate
with the sample standard
deviation, S
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Determining Sample
SizeTo determine the required sample size forthe proportion, you must know:
The desired level of confidence (1 - ),
which determines the critical Z valueThe acceptable sampling error, e
The true proportion of successes,
can be estimated with a pilot sample,
if necessary (or conservatively use
= 0.5)
( )continued
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Ethical IssuesA confidence interval estimate (reflectingsampling error) should always be included
when reporting a point estimate
The level of confidence should always bereported
The sample size should be reported
An interpretation of the confidence intervalestimate should also be provided
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Random Sampling Error andSample Size are Related
As n increases, E decreases at a decreasing rate
costs & non sampling errors increase
$
NSample size
small large
R
andom
Sam p
le
e
rror
Large
Diminishingreturns: randomsampling error isinverselyproportional to the
square root ofn
.
Costs
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Random Error andSample SizeRandom sampling error varies with samples
of different sizes. -Increases in sample sizereduce sampling error at a decreasing rate.
Diminishing returns - random sampling error isinversely proportional to the square root ofn.
Statistical Information Needed to Determine Sample Size for Questions InvolvingMeans
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e erm n ng amp eSize on the Basis of
JudgmentManagerial Judgments:
Setting a sample size that is similar those in
previous studies to provide comparison withother researchers judgments
Selecting the item, question, or characteristicthat will produce the largest sample size.
Collecting a large enough sample to ensurethat subgroup comparisons are reliable.
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SummaryDetermining sample size.Sampling error.
Determining sample size if is unknown.Discus Ethical Issues.
Determining sample size on the basis ofjudgment.
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Insert a thank you slide here