mY Presentation01

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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


nZX

nZe =

Sampling error( )margin of error


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Determining SampleSize

For theMean


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

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