Sampling techniques And Sampling Distributions

Posted On :
Aug162011
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Article Word Count :
2169


Population is the totality of the observations made on all the objects(under investigation) possessing some
common specific characteristics, which are of particular interest to researchers.
The population is the aggregate of the elements and these elements are the basic units that comprise and

1:Population:
Population is the totality of the observations made on all the objects(under investigation) possessing some
common specific characteristics, which are of particular interest to researchers.
The population is the aggregate of the elements and these elements are the basic units that comprise and
define a population.The population must be defined in terms of
(1) Content, (2) Unit, (3) Extent, (4) Time
For instance,the students of the first year class at a given college,the characteristics to be investigated
may be score received by each student in a college entrance examinations,in a given year.
Population may be finite or infinite.
(i)Finite Population:
A population is said to be finite if it includes a limited number of elementary units.
Examples of a finite population are:
The heights of all the students enrolled at a college in a given
year,the wages of all employees of a steell mill in a given year,the amount of money spend by each
student in an engineering university in a given academic year,or the grading of items as defective and
nondefective that are produced by an industry on a given day.
(ii):Infinite Population:
A population is said to be infinite if it consist of unlimited number of elementary units.Atleast hypothetically,
there is no limit to the no of units it can include.
Examples of a infinite population are:
The weights at birth of all human beings,the result obtained by rolling of
die,the lifetime of all the bulbs produced in a production process that operates indefinitely under given
manufacturing conditions.
2: Sample:
A sample is the part of production which is selected eith the expectation that it will represent
the characteristics of the population.
(i):Sampling:
Sampling is a procedure of selecting a representative sample from a given population.
(ii):Sample survey versus complete enumeration:
The collection of information from a part of the population is called making a sample survey.
The collection of information from all elements in a population is called taking a census or making a complete enumeration.
(iii):Purpose of sampling:
There are basic purposes of sampling are:
(a) To obtain maximum information about the characteristics of the population with minimum cost,time and effort.
(b) To find the reliability of the estimates derived from the sample.
(iv):Advantages of sampling:
(a) Time saving:
A sample involves lesser amount of time and energy than a complete enumeration both in the execution and the
analysis of data.This is a vital consideration ehen the information is urgently needed as the results from a sample
survey are more readily available.
(b) Economic:
A sample survey requires less expenses and labour as compared to a complete census because the cost
of covering only a fraction will be lower than that of covering the whole population.
(c) Accuracy:
A sample survey provides the results which are almost as accurate as those obtained by complete census.
A properly designed and carefully executed sample survey will provide even better result.
(d) Feasibility:
Sometimes the data are obtained by tests that are destructive.For example,to tkhow the average life of
certain type of electric bulb,we shall take a sample of these bulbs and keep them on until they burn out.
we cannot think of testing the whole lot.In testing blood of a patient we donot drain the entire blood out
of him but examine just a few drops.Sampling may be the only means available for obtaining the desired
information when the population is infinite or inaccessible.In such cases complete enumeration would
neither be physically possible nor practically feasible..
Whatever be the merits of sampling,it cannot totally replace a complete census.A census is a record of
nation's history and its importance has to be given due acknowledgement.
(v): Limitations of sampling:
If the basic fact of each and every unit in the production are needed,census become indispensable.For Example,
the list of income tax payers is prepared very carefully,the list of voters is prepared to include the name of each and
every voter,or an inventoryof all goods and stocks necessary to know the total amount of stocks of firm.


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