Sampling and Sampling Distribution

1. Sampling & Sampling
Distribution
By:
Dr. Parveen Vashisth
Assistant Professor
CDLU Sirsa

2. Data is Generally collected into two ways:
1. Completed enumeration Survey or Census
Method
2. Sampling Method
Census Method:
Under this method data is collected from each &
every unit (person, household, field, shop,
factory etc.) belonging to the population or
universe.

3. Advantages of Census Method:
1. Information can be obtained from each and
every unit.
2. Greater Accuracy.
Sampling Method
Under this method, instead of every unit of the
population only a part of the population is
studied and conclusions are drawn on that basis
for the entire population.

4. A sampling is not studied for its own shake. The
basic objective of its study is to draw inference
about the population. We can say, sampling is the
only tool which helps to know the characteristics of
the universe or population by examining only a little
part of it.
Principles of Sampling:
1. Principle of Statistical Regulatory: A large
number of items chosen at random from large
group are almost sure on the average to possess
the characteristics of the large group.
2. Principle of Inertia of Large Number: Large the
size of Sample, more accurate the results.

5. Methods of Sampling:
A. Random Sampling:
i. Simple Random Sampling
ii. Stratified Sampling
iii. Systematic Sampling
iv. Multi-Stage Sampling
B. Non- random Sampling
i. Judgment Sampling
ii. Quota Sampling

6. i. Simple Random Sampling:
It refers to the sampling technique in
which each and every item of the population is
given an equal chance of being included in the
sample. The selection is free from personal bias
because the investigator does not exercise his
direction of presence in the choice of items.
Methods of Obtaining a Simple Random
Sampling:
a. Lottery Method
b. Table of Random Numbers

7. ii. Stratified Sampling:
It is one of the restricted random methods
which, by using available information
concerning the data attempts to design a more
efficient sample than that obtained by the
simple random procedure. The process of
stratification requires that the population may
be divided into homogeneous groups or classes
called Strata. Then a sample may be taken from
each group by simple random method and
resulting sample is called Stratified Sample.
*Strata is the group with same characteristics.

8. iii. Systematic Sampling:
The method is to select every ith* item from the
list where ‘i’ is the sampling interval. The
starting point between the first and ith item is
selected at rendom.
For e.g.:- from 100 students to draw the sample
size of 20 students, we must take every 5th
student as a sample.

9. iv. Multi-stage Sampling:
A sampling procedure which is carried out in
several stages. At first, the sample is divided by
random sampling, then selected first stage units
again by some suitable method which may be
the same or different from the method
employed for the first stage units.
For e.g.:- A country is divided in States then in
districts then in tehsil and then in villages.

10. Non-Random Sampling:
i. Judgment Sampling:
In this method the choice of sample items
depends on the judgment of the investigator.
The investigator exercises his judgment in the
choice of sample items.
For e.g.:- if a sample of 10 students is selected
from 100 students, I will select the students as
per my opinion who represent the whole class.

11. ii. Quota Sampling:
It’s just like a judgment sampling. In this
sampling, quotas are set up according to given
criteria, but within quotas the selection of
sample items depends on personal judgment.
For e.g.:- from 100 students of MBA 50 male and
50 female. Out of 50 male 25 from 1st year and
25 from 2nd year and same for female. Out of 25
male 15 from MBA Gen and 10 from MBA Hons.