SAMPLING TECHNIQUES

SAMPLING

Procedure by which some members of a given population are selected as representatives of the entire population.

UNIVERSEthe larger group from which individuals are selected to participate in a study

SAMPLEthe representatives selected for a study whose characteristics exemplify the larger group from which they were selected

PURPOSE OF SAMPLING To gather data about the population in order to make an inference that can be generalized to the population

POPULATION

SAMPLE

INFERENCE

Process Of SamplingDefine the Population

Develop Sampling Frame

Select a Sampling Method

Determine Sample Size

Execute the Sampling Process

Define the Population

Develop Sampling Frame

Select a Sampling Method

Determine the Sample Size

Execute the Sampling Process

The Sampling Process

Sampling and representativeness

Sample

Target Population

SamplingPopulation

Target Population Sampling Population Sample

Sampling Techniques

FixedVs

Sequentialsampling

AttributesVs

Variables Sampling

ProbabilityVs

Non-probability sampling

PROBABILITY SAMPLING

Every element in the target population or universe [sampling frame] has equal probability of being chosen in the sample for the survey being conducted.

Scientific, operationally convenient and simple in theory.

Results may be generalized.

NON-PROBABILITY SAMPLING

Every element in the universe [sampling frame] does not have equal probability of being chosen in the sample.

Operationally convenient and simple in theory.

Results may not be generalized.

CLASSIFICATION OF SAMPLING TECHNIQUES

Sampling Methods

Probability Sampling Methods

Simple Random

Sampling Stratified Random

Sampling

Systematic Random

Sampling

Multistage

Random Sampling

Cluster Sampling

Area Samplin

g

Non-probability Sampling Methods

Convenience Sampling

Judgment Sampling

Quota Samplin

gOther

Sampling

Methods

SIMPLE RANDOM SAMPLINGSimple random sampling is a method of probability sampling in which every unit has an equal non zero chance of being selected for the sample.

Methods of selecting random sample:1. Lottery Method2. Tables of Random Numbers

STRATIFIED RANDOM SAMPLING

Stratified random sampling is a method of probability sampling in which the population is divided into different subgroups and samples are selected from each of them.

Steps:-All units of population are divided into different

stratas in accordance with their characteristics.Using random sampling, sample items are

selected from each stratum.

Systematic Random Sampling or Quasi-Random Sampling

Systematic random sampling is a method of probability sampling in which the defined target population is ordered and the 1st unit of sample is selected at random and rest of the sample is selected according to position using a skip interval (every Kth item)

K = N n

Where, K = Sampling/ Skip interval N = Universe/ Population Size n = Sample Size

 

MULTISTAGE RANDOM SAMPLING

Used in large scale investigationsFirst stage- preparation of large sized

sampling units Randomly selecting a certain numberSecond stage- Another list prepared from

themSub-samples drawn by random sampling

CLUSTER SAMPLINGThe process of randomly selecting intact groups, not individuals, within the defined population sharing similar characteristics

Steps :-1. Defined population is divided into number of

mutually exclusive and collectively exhaustive subgroups or clusters

2. Select an independent simple random sample of clusters.

Area SamplingOne special type of cluster sampling is called

area sampling, where pieces of geographical areas such as districts, housing blocks or townships are selected.

Area sampling could be one-stage, two-stage, or multi-stage.

Generally used by Govt. agencies and agricultural statistics.

Non-probabilitySampling Methods

Convenience samplingthe process of including

whoever happens to be available at the time…called “accidental” or “haphazard” sampling.

Purposive samplingthe process whereby

the researcher selects a sample based on experience or knowledge of the group to be sampled…called “judgment” sampling

Quota samplingthe process whereby a

researcher gathers data from individuals possessing identified characteristics and quotas

Other Non-probability Sampling Methods

Intensity sampling: selecting participants who

permit study of different levels of the research topic

Homogeneous sampling: selecting participants who are very similar in experience, perspective, or outlook

Criterion sampling: selecting all cases that meet some pre-defined characteristic

Snowball sampling relies upon respondent referrals of others with like characteristics

Factors to Consider in Sample Design

Research objectives Degree of accuracy

Resources Time frame

Knowledge oftarget population Research scope

Statistical analysis needs

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