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SAMPLING TECHNIQUES

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SAMPLING

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

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UNIVERSE

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

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SAMPLE

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

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� 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

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Process Of Sampling

Define the Population

Develop Sampling Frame

Select a Sampling Method

Determine Sample Size

Execute the Sampling Process

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Define the Population

Develop Sampling Frame

Select a Sampling Method

Determine the Sample Size

Execute the Sampling Process

The Sampling Process

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Sampling and representativeness

Sample

Target Population

Sampling

Population

Target Population 🡺 Sampling Population 🡺 Sample

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Sampling Techniques

Fixed

Vs

Sequential

sampling

Attributes

Vs

Variables

Sampling

Probability

Vs

Non-probability

sampling

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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.

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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.

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CLASSIFICATION OF SAMPLING TECHNIQUES

Sampling Methods

Probability Sampling Methods

Simple Random Sampling

Stratified Random Sampling

Systematic Random Sampling

Multistage Random Sampling

Cluster Sampling

Area Sampling

Non-probability Sampling Methods

Convenience Sampling

Judgment Sampling

Quota Sampling

Other Sampling Methods

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SIMPLE RANDOM SAMPLING

Simple 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 Method
  2. Tables of Random Numbers

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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.

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��������� Systematic Random Sampling �or Quasi-Random Sampling

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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)

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K = N

n

Where, K = Sampling/ Skip interval

N = Universe/ Population Size

n = Sample Size

 

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MULTISTAGE RANDOM SAMPLING

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  • Used in large scale investigations
  • First stage- preparation of large sized sampling units
  • Randomly selecting a certain number
  • Second stage- Another list prepared from them
  • Sub-samples drawn by random sampling

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CLUSTER SAMPLING

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

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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.

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Area Sampling

  • One 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.

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Non-probability

Sampling

Methods

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Convenience sampling

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

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Purposive sampling

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

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Quota sampling

the process whereby a researcher gathers data from individuals possessing identified characteristics and quotas

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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

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Factors to Consider in Sample Design

Research objectives

Degree of accuracy

Resources

Time frame

Knowledge of

target population

Research scope

Statistical analysis needs

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