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chosen from the population. A finite subset of statistical individuals
defined in a population is called a sample. The number of units in a
sample is called the sample size.
The constituents of a population which are individuals to be
sampled from the population and cannot be further subdivided for
the purpose of the sampling at a time are called sampling units. For
example, to know the average income per family, the head of the
family is a sampling unit. To know the average yield of rice, each
farm owner’ s yield of rice is a sampling unit.
For adopting any sampling procedure it is essential to have
a list identifying each sampling unit by a number. Such a list or
map is called sampling frame. A list of voters, a list of house
holders, a list of villages in a district, a list of farmers etc. are a few
examples of sampling frame.
2.3.2 Reasons for selecting a sample:
Sampling is inevitable in the following situations:
1. Complete enumerations are practically impossible when the
population is infinite.
2. When the results are required in a short time.
3. When the area of survey is wide.
4. When resources for survey are limited particularly in respect
of money and trained persons.
5. When the item or unit is destroyed under investigation.
2.3.3 Parameters and statistics:
We can describe samples and populations by using
measures such as the mean, median, mode and standard deviation.
When these terms describe the characteristics of a population, they
are called parameters. When they describe the characteristics of a
sample, they are called statistics. A parameter is a characteristic of
a population and a statistic is a characteristic of a sample. Since
samples are subsets of population statistics provide estimates of the
13 parameters. That is, when the parameters are unknown, they are
estimated from the values of the statistics.
In general, we use Greek or capital letters for population
parameters and lower case Roman letters to denote sample
statistics. [N, µ, σ, are the sta...
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- Winter '08