Tata Tulis dan Komunikasi Ilmiah - eko.staff.uns.ac.id · Cluster sampling Suppose we want to...

Tata Tulis danKomunikasi Ilmiah

Desain Sampel

Dr. Eko Pujiyanto , S.Si., M.T.

Materi1. Sensus dan survei sampel

2. Langkah-langkah dalam desain sampling,

3. Kriteria memilih prosedur sampling,

4. Karakteristik desain sampel yang baik, 4. Karakteristik desain sampel yang baik,

5. Tipe desain sampel

6. Lampiran : Menentukan jumlah sampel

Jurusan Teknik Industri - Universitas Sebelas Maret

Sensus dan survei sampel

� Semua objek riset berada di alam atau populasi

� Sensus adalah enumerasi semua data dalam populasi.

� Survei sampel adalah memilih secara selektif data yang terdapat dalam populasi

Census


Populasi dan sampel

Population of Interest

N ~ ( μ , σ )

Sample

Population Sample

Parameter Statistic

N ~ ( μ , σ )

sx ,


Steps In Sample Design

1. Type of universe (population)

2. Sampling unit

3. Sampling frame

4. Size of sample4. Size of sample

5. Parameters of interest

6. Budgetary constraint

7. Sampling procedure


Steps In Sample Design


Criteria Of Selecting

A Sampling Procedure

� Researcher must keep in view the two

causes of incorrect inferences :

� Systematic bias

� Sampling error

A systematic bias �results from errors � A systematic bias �results from errors

in the sampling procedures, and it

cannot be reduced or eliminated by

increasing the sample size.




Systematic bias is the result of one or

more of the following factors :

1. Inappropriate sampling frame

2. Defective measuring device

3. Non-respondents

4. Indeterminancy principle

5. Natural bias in the reporting of data




1. Sampling errors are the random

variations in the sample estimates

around the true population

parameters.

2. Sampling error decreases with the 2. Sampling error decreases with the

increase in the size of the sample.

3. Sampling error can be measured for

a given sample design and size.


Characteristics Of

A Good Sample Design1. Sample design must result in a truly

representative sample.2. Sample design must be such which results

in a small sampling error.3. Sample design must be viable in the context

of funds available for the research study.Sample design must be such so that 4. Sample design must be such so that systematic bias can be controlled in a better way.

5. Sample should be such that the results of the sample study can be applied, in general, for the universe with a reasonable level of confidence.


Types of Sample Design


Non-probability sampling

� Sampling procedure which does not afford any basis for estimating the probability that each item in the population has of being included in the sample.

� Items for the sample are selected deliberately by the researcher.researcher.

� Types non-probability sampling

1. Convenience

2. Judgment

3. Quota

4. Snowball


Non-probability sampling1. Convenience sampling

� Also called haphazard or accidental sampling

� The sampling procedure of obtaining the people or units that are most conveniently available

2. Judgment Sampling2. Judgment Sampling

� Also called purposive sampling

� An experienced individual selects the sample based on his or her judgment about some appropriate characteristics required of the sample member


Non-probability sampling3. Quota sampling

� Ensures that the various subgroups in a population are represented on pertinent sample characteristics

� To the exact extent that the investigators desire

� It should not be confused with stratified sampling.

Snowball Sampling4. Snowball Sampling� A variety of procedures

� Initial respondents are selected by probability methods

� Additional respondents are obtained from information provided by the initial respondents


Probability sampling� Also known as ‘random sampling’ or

‘chance sampling’.

� Every item of the universe has an equal

chance of inclusion in the sample.

� Ensures the law of Statistical Regularity � Ensures the law of Statistical Regularity

which states that if on an average the

sample chosen is a random one, the

sample will have the same composition

and characteristics as the universe


Types probability sampling1. Simple Random Sampling

2. Systematic Sampling

3. Stratified Sampling

4. Cluster Sampling4. Cluster Sampling

5. Area sampling

6. Multistage Sampling

7. Sampling with probability proportional to size

8. Sequential sampling


Simple Random Sampling� A sampling procedure that ensures that each

element in the population will have an equal chance of being included in the sample.

� Various statisticians like Tippett, Yates, Fisher have prepared tables of random numbers which can be prepared tables of random numbers which can be used for selecting a random sample.


Systematic Sampling� To select every i-th item on a list

� Only the first unit is selected randomly and the remaining units of the sample are selected at fixed intervals.

It is an easier and less costlier method of � It is an easier and less costlier method of sampling and can be conveniently used even in case of large populations.


Stratified sampling

� Generally applied in order to obtain a representative sample

� Subsamples are drawn within different strata

� Each stratum is more or less equal on some characteristiccharacteristic

� The results in more reliable and detailed information.


Stratified sampling

Three questions are highly relevant in

the context of stratified sampling

1. How to form strata?

2. How should items be selected from each

stratum?stratum?

3. How many items be selected from each

stratum or how to allocate the sample size

of each stratum?


Stratified sampling

1. How to form strata?

Various strata be formed in such a way as to ensure elements being most homogeneous within each stratum and most heterogeneous between the different strata.the different strata.

2. How should items be selected from each stratum?

Systematic sampling can be used if it is considered more appropriate in certain situations


Stratified sampling

3. How many items be selected from each stratum

� Proportional allocation under which the sizes of the samples from the different strata are kept proportional to the sizes of the strata.proportional to the sizes of the strata.

� To illustrate it, let us suppose that we want a sample of size n= 30 to be drawn from a population of size N= 8000 which is divided into three strata of size N1= 4000, N2= 2400 and N3= 1600.


Stratified sampling



Stratified sampling


� In cases where strata differ not only in size but also in variability


Stratified sampling


Cluster sampling

� A sample can be taken is to divide the area into a number of smaller non-overlapping areas and then to randomly select a number of these smaller areas (clusters), with the ultimate sample consisting of all (or samples of) units in these small consisting of all (or samples of) units in these small areas or clusters.

� The purpose of cluster sampling is to sample economically while retaining the characteristics of a probability sample.


Cluster sampling

� Suppose we want to estimate the proportion of machine-parts in an inventory which are defective.

� Also assume that there are 20000 machine parts in the inventory at a given point of time, stored in 400 cases of 50 each. 400 cases of 50 each.

� Now using a cluster sampling, we would consider the 400 cases as clusters and randomly select ‘n’ cases and examine all the machine-parts in each randomly selected case.


Area sampling

� If clusters happen to be some geographic subdivisions, in that case cluster sampling is better known as area sampling


Multistage sampling

� Further development of the principle of cluster sampling.

� Suppose we want to investigate the working efficiency of nationalised banks in India and we want to take a sample of few banks for this purpose. sample of few banks for this purpose.

� The first stage is to select large primary sampling unit such as states in a country.

� Then we may select certain districts and interview all banks in the chosen districts.

� This would represent a two-stage sampling design with the ultimate sampling units being clusters of districts.


Sampling with probability proportional to size

� In case the cluster sampling units do not have the same number or approximately the same number of elements.


Sampling with probability proportional to size


Sequential Sampling

� This sampling design is some what complex sample design.

� The ultimate size of the sample under this technique is not fixed in advance, but is determined according to mathematical decision rules on the basis of to mathematical decision rules on the basis of information yielded as survey progresses.

� This is usually adopted in case of acceptance sampling plan in context of statistical quality control.


LampiranMenentukan ukuran sampel

Syarat


Lampiran

( Menentukan ukuran sampel )


Referensi� Khotari, C.R., 2004, Research Methodology: Methods and

Techniques, New Age International (P) Ltd., Publishers. ( Chapter 4)


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