NON -PROBABILITYSAMPLING
NON – PROBABILITY SAMPLING
Non-probability sampling is a sampling technique where the odds of any member being selected for a sample cannot be calculated. It’s the opposite of probability sampling, where you can calculate the odds.
For example, one person could have a 10% chance of being selected and another person could have a 50% chance of being selected. It’s non-probability sampling when you can’t calculate the odds at all
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WHEN? WHY? TO USE NON-PROBABILITY SAMPLING
1. This type of sampling can be used when demonstrating that a particular trait exists in the population.
2. It can also be used when the researcher aims to do a qualitative, pilot or exploratory study.
3. It can be used when randomization is impossible like when the population is almost limitless.
4. It can be used when the research does not aim to generate results that will be used to create generalizations pertaining to the entire population.
5. It is also useful when the researcher has limited budget, time and workforce. 5
Advantages
Possibility to reflect the descriptive comments about the sample
Cost-effectiveness and time-effectiveness
Effective when it is unfeasible or impractical to conduct probability sampling
PRONS & CONS
Disadvantages
Unknown proportion i.e. lack of representation of the entire population
Lower level of generalization of research findings compared to probability sampling
Difficulties in estimating sampling variability and identifying possible bias
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Non-Probability Sampling
Conven-ience
sampling
Purposive sampling
Quota sampling
Snowball sampling
4 Methods
CONVENIENCE SAMPLING
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1Also know as Accidental Sampling
“ In convenience sampling no inclusion criteria identified prior to the selection of subjects. The sample is selected in anyway for the sake of easiness and convenience
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EXAMPLES
▰ Facebook polls
▰ Pepsi Challenge
▰ Feedback system in big companies
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Advantages
Simplicity of sampling and the ease of research
Helpful for pilot studies and for hypothesis generation
Data collection can be done in short duration of time
Cheapest to implement
PRONS & CONS
Disadvantages
Highly vulnerable to selection bias and influences beyond the control of the researcher
High level of sampling error
Studies that use convenience sampling have little credibility due to reasons above
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PURPOSIVE SAMPLING
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2Also known as judgment, selective or subjective sampling
“ The researchers or experts obtain a representative sample by using a sound judgment, which will result in saving time and money
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EXAMPLES
▰ TV reporters stopping certain individuals on the street in order to ask their opinions about GST on insurance (this can be asked to only to an educated man).
▰ A study of importance of exposure in colleges (this can be asked to only those students who has experienced exposure in college).
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Advantages
Cost-effective and time-effective
Requires limited number of primary data sources
One of the most time-effective sampling methods available
PRONS & CONS
Disadvantages
Vulnerability to errors in judgment by researcher
Low level of reliability and high levels of bias.
Inability to generalize research findings
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QUOTASAMPLING
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3It has two types controlled and uncontrolled
“ A method of gathering representative data from a group to ensure that sample group represents certain features of the population chosen by the researcher.
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HOW TO PERFORM QUOTA SAMPLING
1. Dividing the population into specific groups
Virgin Media employees in the UK as the sampling frame need to be divided into the following five groups according to their cultural background:
European, Asian (India), Asian (China), Black (African) and Other
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2. Calculating a quota for each group
Suppose you take 30 representatives from each group making total of 150.
3. Determine specific condition(s) to be met and quota in each group
Both genders, males and females need to be represented equally i.e. 15 each.
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Advantages
Quota sampling is good when you are pressed for time, since primary data collection can be done in shorter time
This sampling method can save costs and time.
It can also be done in absence of sampling frame
PRONS & CONS
Disadvantages
We can’t calculate sampling error and the projection of the research findings
There is disproportionately represented in the final sample group
It may suffer from researcher incompetency and/or lack of experience
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2 TYPES QUOTA SAMPLING
Uncontrolled sampling, in this the researcher is free to choose sample group members according to his/her will.
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Controlled Uncontrolled
Controlled sampling involves introduction of certain restrictions in order to limit researcher’s choice of samples.
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SNOWBALLSAMPLING
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4Also known as cold-calling, chain, chain-referral, and referral sampling.
“ Snowball sampling is where research participants recruit other participants for a test or study. It is used where potential participants are hard to find
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INTERESING NAME !!
It’s called snowball sampling because (in theory) once you have the ball rolling, it picks up more “snow” along the way and becomes larger and larger.
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EXAMPLES
▰ A study on investigating cheating on exams
▰ Company that involves primary data collection from employees of that company.
▰ Mostly used in taking surveys with the help of questionnaire.
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3 PATTERNS OF SNOWBALL SAMPLING
Exponential non-discriminative snowball sampling
The first subject recruited to the sample group provides multiple referrals.
Exponential discriminative snowball sampling
Subjects give multiple referrals, however, only one new subject is recruited among them.
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Linear snowball sampling
Formation of a sample group starts with only one subject and the subject provides only one referral.
Advantages
The ability to recruit hidden populations
The possibility to collect primary data in low cost
It can be completed in a short duration of time
A very little planning is required to start sampling process
PRONS & CONS
Disadvantages
Oversampling can be done
Respondents may be hesitant to ask all questions
It is not possible to determine the actual pattern of distribution of population.
It is not possible to determine the sampling error 31
REFERENCES
https://research-methodology.net
http://www.statisticshowto.com
https://images.google.com/
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