Sampling

•Sampling•Population•Elements•Subject•Sampling unit•Sampling process•Sampling units

Sampling •The process of selecting right individual

objects, or events as representative for the entire population is known as sampling.

For example•Sensex-30 companies •Nifty- 50 companies

Population•The population refers to the entire group

of people, events or things of interest that researcher wishes to investigate and wants to make inferences.

For example•If researcher wants to know the

investment pattern of Mumbai city then all residents of Mumbai will be the population.

Element•An element is a single member of the

population.e.g.•Total students of GICED is 1800, then

each student will be the element.

Sample• It is a subject of the population• It comprises some members selected from it• In other words, some, but not all elements of

the population form sample.• By studying the sample, the researcher should

be able to draw conclusion that are generalized to the population of interest

E.g. • Sensex-BSE• Nifty-NSE

Sampling unit•It is the element or set of element that is

available for set selection in some stage of the sampling process

Subject•It is a single member of the sample just as

an element of the population.

Reasons for sampling

•Practically impossible to collect data from, or examine every element

•Even it is possible, it is prohibitive in terms of time, cost and human resources

•Study of sample rather than population is also sometimes likely to produce more reliable data especially when a large number of elements is involved

•E.g. election survey by media

Representative Sample -  

•σ 2

•σ

•Population – µ •σ 2

•σ

Sampling process

•Define population•Determine sample frame•Determine sample design•Determine appropriate sample size•Execute sampling process

Define population•It must be defined in terms of elements,

geographical boundaries and time

Determine sample frame•It is a representation of all the elements

in the population from which the sample is drawn

E.g.•The payroll of an organization would

serve as the sampling frame if its members are to be studied

Sampling designTwo major types of sampling design•Probability•Non probability

Probability•The elements in the population have some

known, non-zero chance or probability of being selected as a sample object

•This design is used when the representative of the sample is of importance in the interest of wider generalizability

•Non probability•Elements in the population do not have a

known or predetermined chance of being selected as a subject

•When time and other factors, rather than generalizability, become critical, non probability sampling is generally used

Determine sample size• Is a large sample better than a small sample?•Decision about how large the sample size

should be a very difficult one.•We can summarize the factors affecting

factors affecting decision on sample size as •Research objective•Cost and time constraint•Amount of the variability in the population

itself

Probability sampling

1. Unrestricted or simple random sampling2. Restricted or complex probability

sampling•Systematic sampling•Stratified random sampling•Cluster sampling •Double sampling or Area sampling

Unrestricted or simple random sampling•In this sampling every element in the

population has known and equal chance of being selected as a subject

•This sampling design, has the least bias and offers the most generalizability

•However this sampling process could become cumbersome and expenive

Restricted or complex probability sampling•These probability sampling procedures

offer a viable and sometimes more efficient design

•More information can be obtained

Systematic samplingIt involves drawing every nth element in the

population starting with randomly chosen element between 1 & nth element

Stratified random sampling•It involves a process of segregation

followed by random selection of subject from each stratum

Cluster sampling•In this target population is first divided

into clusters•A specific cluster sampling is area

sampling

•Double sampling•When further information is needed from

subset of the first group from which some information has already been collected for the same study.

Non probability sampling

•There are two types1. Convenience2. Purposive

Convenience•Collection of information from members

of the population who are conveniently available to provide it.

Purposive1. Judgment2. Quota

1. Judgment•Most advantageously placed•In the best position to provide information

required

Quota•Certain group