Unformatted text preview: ccording to its size.
In nonproportionate sample, equal representation is given
to all the substrata regardless of their existence in the population.
Example 2:
A sample of 50 students is to be drawn from a population
consisting of 500 students belonging to two institutions A and B.
The number of students in the institution A is 200 and the
institution B is 300. How will you draw the sample using
proportional allocation?
Solution:
There are two strata in this case with sizes N1 = 200 and N2 = 300
and the total population N = N1 + N2 = 500
The sample size is 50.
If n1 and n2 are the sample sizes,
n1 = n
50
×200=20
×N1 =
N
500 n2 = n
50
×300=30
×N2 =
N
500 The sample sizes are 20 from A and 30 from B. Then the
units from each institution are to be selected by simple random
sampling.
Merits and limitations of stratified sampling:
Merits:
1. It is more representative.
2. It ensures greater accuracy.
20 3. It is easy to administer as the universe is sub  divided.
4. Greater geographical concentration reduces time and
expenses.
5. When the original population is badly skewed, this method is
appropriate.
6. For non – homogeneous population, it may field good results.
Limitations:
1. To divide the population into homogeneous strata, it requires
more money, time and statistical experience which is a
difficult one.
2. Improper stratification leads to bias, if the different strata
overlap such a sample will not be a representative one.
2.5.3 Systematic Sampling:
This method is widely employed because of its ease and
convenience. A frequently used method of sampling when a
complete list of the population is available is systematic sampling.
It is also called Quasirandom sampling.
Selection procedure:
The whole sample selection is based on just a random start .
The first unit is selected with the help of random numbers and the
rest get selected automatically according to some pre designed
pattern is known as systematic sampling. With systematic random
sampling every Kth element in the frame is selected for the sample,
with the starting point among the first K ele...
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 Winter '08
 Moshiri
 Business, Statistics

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