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Sample : A sample, in the context of scientific research, commercial analysis and statistics, is a representative subset of a population.

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population: population: The whole number of people or inhabitants in a country or region or study group.

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Sampling: Sampling is the process or technique of selecting a representative part of a population for the purpose of determining parameters or characteristics of the whole population.

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Principle of sample survey: There are four Principle of sample survey:

(i) Law of statistical regularity

(ii) Principle of inertia

(iii) Principle of Optimization

(iv) Principle of validity

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Errors in sample survey: There are two types of error

(i) Sampling error

(ii) Non-Sampling error

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Statistic: The statistical measurement of sample is knowns as statistic. for example mean of sample, standard deviation of sample and etc.

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Parameter: The statistical measurement of population is known as Parameter. for example mean of population, S.D. of population and etc.

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Sampling Fluctuation: The variation in the values of a statistic is termed as sampling fluctuation

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Standard Error: The standard deviation of statistic is known as standard error. It is inversely proportional to the square root of sample size.

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Sampling with replacement:

A sampling is known as with replacement if selected unit is replace into the population before drawing the next unit. In this a unit is selected more than one time in possible sample.

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Sampling Without Replacement:

A sampling is said to be without replacement if selected unit is not replace into the population before next unit. In this case unit is selected one time & possible sample.

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Sample size:

(i) Total number of sample withreplacement: Nⁿ

(ii) Total number of sample without replacement: _NCⁿ

Where N = polulation size, n = sample space.

(iii) Formula to calculate sample size:

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Type of sampling:

(i) Probability sampling

(ii) Non-probability sampling

(iii) Mixed sampling

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Type of probability sampling

(i) Simple random sampling

(ii) Stratified sampling

(iii) Multi-stage sampling

(iv) Quota sampling

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Mixed sampling

Systematic sampling is the example of Systematic sampling.

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