Unformatted text preview: shall consider the following three methods:
1. Simple random sampling.
2. Stratified random sampling.
3. Systematic random sampling.
1. Simple random sampling:
A simple random sample from finite population is a sample
selected such that each possible sample combination has equal
probability of being chosen. It is also called unrestricted random
sampling.
2. Simple random sampling without replacement:
In this method the population elements can enter the sample
only once (ie) the units once selected is not returned to the
population before the next draw.
3. Simple random sampling with replacement:
In this method the population units may enter the sample
more than once. Simple random sampling may be with or without
replacement.
16 2.5.1 Methods of selection of a simple random sampling:
The following are some methods of selection of a simple
random sampling.
a) Lottery Method:
This is the most popular and simplest method. In this
method all the items of the population are numbered on separate
slips of paper of same size, shape and colour. They are folded and
mixed up in a container. The required numbers of slips are selected
at random for the desire sample size. For example, if we want to
select 5 students, out of 50 students, then we must write their
names or their roll numbers of all the 50 students on slips and mix
them. Then we make a random selection of 5 students.
This method is mostly used in lottery draws. If the universe
is infinite this method is inapplicable.
b) Table of Random numbers:
As the lottery method cannot be used, when the population is
infinite, the alternative method is that of using the table of random
numbers. There are several standard tables of random numbers.
1. Tippett’ s table
2. Fisher and Yates’ table
3. Kendall and Smith’ s table are the three tables among
them.
A random number table is so constructed that all digits 0 to
9 appear independent of each other with equal frequency. If we
have to select a sample from population of size N= 100, then the
numbers can be combin...
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 Winter '08
 Moshiri
 Business, Statistics

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