sampling methods- random, systematic and snowball

SAMPLING TECHNIQUES

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SAMPLING

SIMPLE RANDOM

SYSTEMATIC

SNOW BALL

-SHRUTI NIMBKAR-SONALI KURIL-MUBARAKA .H

SAMPLING TECHNIQUES

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At the end of the session, you will be able to:• Explain probability sampling• Explain Simple random sampling.• State the advantages of Simple random sampling• State the disadvantage of Simple random sampling• Generate examples for Simple random sampling

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Objectives

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• A probability sampling is one in which every individual in the population has a chance of

• being selected in the sample, and this probability can be accurately determined

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Probability Sampling

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• Simple Random sampling is a type of probability sampling.

• Each individual is chosen randomly and entirely by chance

• each individual has the same probability of being chosen at any stage during the sampling process

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Simple random

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ResearcherResearcher

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Model

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• One unit of element is randomly selected from population is the first sample unit

• Then the sample unit is replaced in the population• The second sample is drawn with equal

probability• The procedure is repeated until the requisite

sample units ‘n’ are drawn• The probability of selection of an element remains

unchanged after each draw• The same units could be selected more than once

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Method

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• Each member of the population has an equal chance of being chosen

• Freedom from human bias and classification error

• Only the complete listing of the elements in a population is needed

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Advantages

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• Lead to the assembly of a sample which does not represent the population well

• The probability of errors in sampling increases with decreased sample size

• Data gathering entails a lot of time and labor

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Disadvantages

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Examples

SAMPLING TECHNIQUES

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At the end of the session, you will be able to:• Explain probability sampling.• Explain Systematic random sampling.• State the advantages of Systematic random sampling• State the disadvantage of Systematic random

sampling• Generate examples for Systematic random sampling

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Objectives

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• A method of selecting sample members from a larger population according to a random starting point and at a fixed periodic interval.

• In Systematic sampling the periodic interval is determined beforehand and the starting point is random.

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Systematic Sampling

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MODEL

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• First, the researcher selects a number that is less than the total number of individuals in the population.

• Next, the researcher chooses the sampling interval, which is the standard distance between elements selected in the sample.

• The sampling interval is calculated by dividing the population size by the sample size

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Method

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• Allows to add a systematic element

• The population will be evenly sampled

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Advantages

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• If the researcher doesn’t ensure that the sample equally represents all the members of the population, the statistician will have faulty results

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Disadvantages

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Examples

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• The cricket club wants to know players’ satisfaction about the facilities and coaching expertise it provides. The club is only for teen aged boys. There are 700 boys who are currently members of this club. The authorities have all the players’ names with them but they can not survey all of them because of limited resources. Hence they want a representative sample.

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Scenario

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At the end of the session, you will be able to:

• Explain non-probability sampling.

• Explain Snowball sampling.

• State the advantages of Snowball sampling

• State the disadvantage of Snowball sampling

• Generate examples for Snowball sampling1

Objectives

SAMPLING TECHNIQUES

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• Non-probability sampling is a sampling technique where the samples are gathered

• In a process that does not give all the individuals in the population equal chances of being selected.

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Non-probability

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• Snowball is a type of non-probability sampling technique

• Snowball sampling is choosing the participants to find more participants for making a sample group

• Mostly researchers used this sampling technique where participants are difficult to locate in a general population

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Snowball sampling

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• Snowball sampling technique works as a chaining system

• Participants refer other participants

• There are two important things to remember in Snowball sampling:

1. To find one or more research participant for research

2. To take reference of participant to get more sample size in research

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SAMPLING TECHNIQUES

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Model

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Examples

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• It is a good method to find out hidden population

• Useful to create sample group where it is difficult to find participants

• This method easily gives them identity and motivation

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Advantages

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• It is impossible to find out sampling errors

• Snowball samples cannot be considered as representative of entire population

• Sometimes samples can be bias

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Disadvantages

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The news-paper team wants to study the reasons of

school failures and drop outs in present scenario. For their research they want educational counselors to be their respondents. There is no sample frame available of such people. But the team knows two such persons.

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Scenario

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SAMPLING TECHNIQUES

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