What is sample ? nature of sample, What is sampling ? characteristics of sampling, techniques or types of sampling, probability sampling and it's types , non-probability sampling and it's types,

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What is Sample ?

Sample is the part of population which is representative of that population. A sample is the group of people who take part in the investigation . It is a smaller, manageable version of a larger group. A researcher cannot directly make observation of every individual in the population  for the study , so that's why he select a subset of individuals {sample} . 

 




Example:- Suppose, the total population of the collage is 7000 and a researcher choose only 100 boys and 100 girls for his study . Here 7000 represent whole population or universe and those 200 are the samples of that population .

Definitions:-

" A Sample is a portion of the entire lot of certain kind of objects."  [ Mohsin 1984 ]

" Sample is a selected part which is representative of the whole."  [ Chaplin, 1975, P- 468 ]

" Sample refers to a selection of scores from a total set of scores known as the population." 

                                                                                                        [ Atkinson et.al, 1998. ]

" Sample is a part of a population selected such that it is considered to be representative of the population as a whole."  [ Reber and Reber 2001, P- 642 ] 


What is nature of sample ?

1.     Sample is a part of population.

2.     Limited area

3.     Dependent upon population

4.     Always have relationship with population

5.     Sample is representative of population

6.     Qualitative in nature

What is Sampling ?

Sampling is a process through which selection of a sample takes place. It is a process through which selection of a limited subset or unit takes place for the study. 

Definition:-

" Sampling is the process of selecting a sample." [ Chaplin.1975]

" Sampling refers to the operation of drawing a sample from a population." [ Reber & Reber, 2001, P-642 ]

" Sampling is any portion of a population or universe, as representative of that population or universe."  [ Kerlinger, 2002,P-118 ]

Characteristics of Sampling:-

1.     Representative to the population

2.     Based on probability theory

3.     Homogeneity of population

4.     Adequate size of the sample

5.     Economy of time, labor and money 

6.     Randomization

7.     Free from biases

8.     Free From sampling errors

9.     Relevant to the purpose of the study

10. High reliability

Techniques or Types of Sampling:-





1.     Probability sampling

2.     Non-probability sampling

Probability Sampling:- These type of technique have two basic speciality:- 

  • Sample made by these technique have equal probability unit of population to combine.
  • In sample, all the qualities of population may be present

Definition:-

" Probability sampling is that sampling in which there is all probability that all the characteristics of the population are present in the sample and that each unit of the population has equal probability for its inclusion in the sample." [Author]

" Probability sampling is that sampling in which the events or elements are drawn according to some known probability structure." [ Reber & Reber, P- 642 ]

Merits or advantages of probability sampling:-

  • True representation
  • Equal probability
  • High reliability
  • Free from biases
  • Known probability structure
  • Estimation of sampling error

Demerits or disadvantages of probability sampling:-

  • In probability sampling , knowledge of whole population is must
  • We can't use probability in that place where the population is unknown , because in this sampling the knowledge of population is must
  • This is more money , labor , and time consuming.
  • When we want to study small sample than this sampling is not suitable

Types of probability sampling:-


1.     Random sampling:- 





" Random sample is a sample which has been drawn such that each number or object in the population has an equal probability of being selected." [ Reber & Reber , 2001,P- 642 ]

" Random sampling is that method of drawing a sample so that each member of the population has an equal chance of being selected."  [ Kerlinger ,2000 , P- 118 ]

How random sample is selected ?

  • Lottery method
  • Sequential list method
  • Random number table method
  • Grid method

Merits of random sampling:-

  • Valid representation of the population
  • Equal probability of selection for all units of the population
  • Free from bias
  • Assessment of sampling errors
  • Appropriate for homogeneous population
  • Appropriate for moderate population 
  • Known probability structure 
  • High reliability and validity

Demerits of random sampling:-

  • Inappropriate for heterogeneous population
  • Inappropriate for a very large population
  • Inappropriate for extensive population
  • Effect of biases
  • Instable nature of the selected units
  • Practical difficulties

      2. Stratified sampling:-





" In stratified sampling the population is divided into strata , such as men and women , black and white, and the like, from which random samples are drawn."  [ Kerlinger , 2002 , P- 130 ]

" Stratified sampling is that sampling in which the population as a whole is separated into distinct parts[ strata ] and each is drawn from separately." [ Reber , 1995, P- 660 ]

Merits of stratified sampling:-

  • True representative of population
  • Appropriate for heterogeneous population
  • Appropriate for extensive population
  • Appropriate for very small population
  • Greater precision
  • High predictive validity and reliability

Demerits of stratified sampling:-

  • Difficulty of determining all the units within the population
  • Difficulty of stratification
  • Difficulty of proportion between population units and sample units
  • Time , labor, and money consuming
  • Dynamic nature of the population
  • Possibility of the effect of personal biases

      3. Cluster sampling:-




" Cluster sampling, the most used method in surveys, is the successive random sampling of units, or sets and subsets." [ Kerlinger, 2002, P- 130 ]

Merits of cluster sampling:-

  • Appropriate for very large population
  • Appropriate for very extensive population
  • Time and labor saving
  • Economical
  • Greater precision
  • Appropriate for survey research

Demerits of cluster sampling:-

  • Difficulty of making clusters
  • Effect of biases
  • Partial representation
  • Greater possibility of sampling errors
  • Low reliability and validity

Non-Probability sampling:-

" Non-probability sampling is that sampling in which the probability of each event or element being drawn is not known."  [ Reber, 1995, P- 659 ]

Merits of Non-probability sampling:-

  • Simplicity and ease
  • Appropriate for piolet study
  • Appropriate for ambiguous population
  • Time and labor saving
  • Economical
  • Greater flexibility

Demerits of Non-probability sampling:-

  • Partial representation
  • Lack of randomization
  • Dangers of biases
  • Low reliability and predictive validity

Types of Non-probability sampling:-

1.     Purposive or judgmental sampling:-



" Their weakness can to some extent be mitigated by using knowledge, expensive and care in selecting samples and by replicating studies with different samples." [ Kerlinger , 2002, P- 129 ]

" Another form of non-probability sampling is purposive sampling, which is characterized by the use of judgment and deliberate efforts to obtain representative sample by including presembly typical areas or groups in the sample." 

Merits of purposive sampling:-

  • Simplicity
  • Flexibility
  • Independent from any pressure
  • Time and labor saving

Demerits of purposive sampling:-

  • Lack of representation
  • Biased sample
  • Lack of equal chance for every unit
  • Greater sampling errors
  • Low reliability and validity

      2. Incidental or Accidental sampling:-



" So-called accidental sampling , the weakest form of sampling, is probably also the most frequent." 

[  Kerlinger , 2002, P- 129 ]

Merits of Incidental or Accidental sampling:-

  • Simple 
  • Time and labor saving
  • Economical
  • Appropriate for homogeneous population
  • Appropriate for pilot study

Demerits of Incidental or Accidental sampling:-

  •  Lack of representativeness
  •  Not applicable for probability theory
  • Biased
  • High reliability and validity
  • High precision

       3. Quota sampling:-



" Quota sampling is a variety of stratified sampling in which a specific member of cases [ the quota ] is selected from each situation."  [ Reber, A.S., 1995, P-682 ]

Merits of quota sampling:-

  • Simple
  • Time, labor and money saving
  • More useful than purposive sample
  • Representation

Demerits of quota sampling:-

  • Lack of randomization
  • Personal biases
  • Less reliability and validity

      4. Snowball sampling:-





" Snowball sampling is that sampling in which each person in the sample is asked to provide the names of several other persons, who are then added to the sample and asked to names and so on." 

[ Reber & Reber , 2001, P- 643 ] 

References :-
 

https://www.investopedia.com/terms/s/sample.asp

https://www.simplypsychology.org/sampling.html#:definition%20o

 https://psychology.ucdavis.edu/rainbow/html/fact_sample.html

 https://dictionary.apa.org/sampling

 Book :- Research methods in psychology sociology and education - [ By A.K. Singh ]


Thank you..... 






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