LIAQUAT
MEDICAL
UNIVERSITY

By:

Assist: Prof:
Faculty of Community Medicine & Public Health Sciences
Liaquat University o...
POPULATION
 The

whole group of the individuals
on which the results of the study are
to be generalized is known as
Popul...
 Listing

Sampling Frame

of all the members of the universe
from which the sample is to be taken , is
known as Sampling ...
WHY SAMPLING IS
NECESSARY?
 Convenient.
 Economic.
 Time saving.
 Less resources are required.
 Easy to interpret the...
TYPES OF SAMPLING
• A. Probability Sampling Methods
• B. Non Probability Sampling Methods
SAMPLES TECHNIQUES
A. Probability Sampling Methods
Simple Random
Simple Random
systemic sampling
systemic sampling
Stratif...
B. Non probability
Sampling Methods
Convenience
Convenience
Judgment
Judgment
Quota
Quota
Snowball
Snowball

14-12
1. Simple Random sampling
1. Simple Random sampling
OR Lottery Method



Each element in the population will have
an equa...
Simple random sampling
2. systemic sampling
2. systemic sampling


Selecting unit/ person after a regular
interval

1 - 15
Systematic sampling
3. Stratified
3. Stratified
It involves division of
population in to smaller
groups (homogenous subgroups)
known as “Strat...
1 - 18
4. Cluster
4. Cluster




Here we select a simple random sample of
groups such as a certain number of city
blocks & then...
Cluster sampling
Section 1

Section 2

Section 3

Section 5
Section 4
5. Multistage
5. Multistage
•
•
•
•

Sampling at different stages/ Levels
1. National level
A sample selected in stages, b...
Non probability Methods
NON PROBABILITY
SAMPLING
• Convenient
• Economic
BUT
RESULTS CAN NOT BE GENERALIZED
THEREFORE
Some probability factor is n...
1. Convenience /Accidental/Incidental sampling
1. Convenience /Accidental/Incidental sampling


Involves the use of the m...
2. Judgment /Purposive
2. Judgment /Purposive


The researcher chooses the sample based on
who they think would be approp...
3. Quota
3. Quota
Researcher selects people according to some fixed quota.
OR
Keep going until the sample size is reached
...
4. Snowball
4. Snowball
Get sampled people to nominate others
Researcher collects data on the few members of the
target po...
Sampling Errors
A. Size:

sample size should be large as possible
depends upon feasibility (time, person, importance of da...
THANKYOU
Sampling  by dr najeeb memon
Sampling  by dr najeeb memon
Sampling  by dr najeeb memon
Sampling  by dr najeeb memon
Sampling  by dr najeeb memon
Sampling  by dr najeeb memon
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Sampling by dr najeeb memon

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sampling by Dr: Najeeb Memon LUMHS, Jamshoro Pakistan

email mnajeeb80@gmail.com

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  • Convenience samples are nonprobability samples where the element selection is based on ease of accessibility. They are the least reliable but cheapest and easiest to conduct. Examples include informal pools of friends and neighbors, people responding to an advertised invitation, and “on the street” interviews.
    Judgment sampling is purposive sampling where the researcher arbitrarily selects sample units to conform to some criterion. This is appropriate for the early stages of an exploratory study.
    Quota sampling is also a type of purposive sampling. In this type, relevant characteristics are used to stratify the sample which should improve its representativeness. The logic behind quota sampling is that certain relevant characteristics describe the dimensions of the population. In most quota samples, researchers specify more than one control dimension. Each dimension should have a distribution in the population that can be estimated and be pertinent to the topic studied.
    Snowball sampling means that subsequent participants are referred by the current sample elements. This is useful when respondents are difficult to identify and best located through referral networks. It is also used frequently in qualitative studies.
  • Convenience samples are nonprobability samples where the element selection is based on ease of accessibility. They are the least reliable but cheapest and easiest to conduct. Examples include informal pools of friends and neighbors, people responding to an advertised invitation, and “on the street” interviews.
    Judgment sampling is purposive sampling where the researcher arbitrarily selects sample units to conform to some criterion. This is appropriate for the early stages of an exploratory study.
    Quota sampling is also a type of purposive sampling. In this type, relevant characteristics are used to stratify the sample which should improve its representativeness. The logic behind quota sampling is that certain relevant characteristics describe the dimensions of the population. In most quota samples, researchers specify more than one control dimension. Each dimension should have a distribution in the population that can be estimated and be pertinent to the topic studied.
    Snowball sampling means that subsequent participants are referred by the current sample elements. This is useful when respondents are difficult to identify and best located through referral networks. It is also used frequently in qualitative studies.
  • Sampling by dr najeeb memon

    1. 1. LIAQUAT MEDICAL UNIVERSITY By: Assist: Prof: Faculty of Community Medicine & Public Health Sciences Liaquat University of Medical & Health Sciences (LUMHS) Jamshoro, Sind, Pakistan e mail mnajeeb80@gmail.com
    2. 2. POPULATION  The whole group of the individuals on which the results of the study are to be generalized is known as Population. A of people of interest from whom The entire group the researcher needs to obtain information. SAMPLE  small group of individuals chosen for the study is known as Sample. The selection of a subset of the population
    3. 3.  Listing Sampling Frame of all the members of the universe from which the sample is to be taken , is known as Sampling Frame. Listing of population from which a sample is chosen  Sampling frame should be carefully developed as it affects the results drawn.
    4. 4. WHY SAMPLING IS NECESSARY?  Convenient.  Economic.  Time saving.  Less resources are required.  Easy to interpret the data.
    5. 5. TYPES OF SAMPLING • A. Probability Sampling Methods • B. Non Probability Sampling Methods
    6. 6. SAMPLES TECHNIQUES A. Probability Sampling Methods Simple Random Simple Random systemic sampling systemic sampling Stratified Stratified Cluster Cluster Multistage Multistage 14-11
    7. 7. B. Non probability Sampling Methods Convenience Convenience Judgment Judgment Quota Quota Snowball Snowball 14-12
    8. 8. 1. Simple Random sampling 1. Simple Random sampling OR Lottery Method  Each element in the population will have an equal chance of being included in the sample. No: is given to each of units (Persons/ houses) Table of random Nos: is used Samples selected haphazardly (Each has equal chance of being selected) N = 100 population size, n = 8 sample size E.g:- In Electro roll / Census 1 - 13
    9. 9. Simple random sampling
    10. 10. 2. systemic sampling 2. systemic sampling  Selecting unit/ person after a regular interval 1 - 15
    11. 11. Systematic sampling
    12. 12. 3. Stratified 3. Stratified It involves division of population in to smaller groups (homogenous subgroups) known as “Strata” •Then Simple random sampling OR systematic sampling is applied with each stratum. Example 2 Population is divided on the basis of characteristic of interest in the population E.g. male & female may have different consumption patterns.
    13. 13. 1 - 18
    14. 14. 4. Cluster 4. Cluster   Here we select a simple random sample of groups such as a certain number of city blocks & then select a person each from each block. This technique is more economical than the random selection of persons through out the city.
    15. 15. Cluster sampling Section 1 Section 2 Section 3 Section 5 Section 4
    16. 16. 5. Multistage 5. Multistage • • • • Sampling at different stages/ Levels 1. National level A sample selected in stages, beginning with the most unspecific level (such as regions) and ending with the 2. Provincial level most specific (such as houses on selected city blocks). 3. District level 
    17. 17. Non probability Methods
    18. 18. NON PROBABILITY SAMPLING • Convenient • Economic BUT RESULTS CAN NOT BE GENERALIZED THEREFORE Some probability factor is needed to be imposed to ensure a degree of representation in the sample.
    19. 19. 1. Convenience /Accidental/Incidental sampling 1. Convenience /Accidental/Incidental sampling  Involves the use of the most convenient & readily available subjects for sample.  A convenience sample is a sample where the patients are selected, in part or in whole, at the convenience of the researcher . Example:  Male on street interviews  Teacher uses students
    20. 20. 2. Judgment /Purposive 2. Judgment /Purposive  The researcher chooses the sample based on who they think would be appropriate for the study.
    21. 21. 3. Quota 3. Quota Researcher selects people according to some fixed quota. OR Keep going until the sample size is reached if you are a researcher conducting a national quota sample, you might need to know what proportion of the population is male(40) and what proportion is female (60) as well as what proportions of each gender fall into different age categories, race or ethnic categories, educational categories, etc. Male 40 Female 60 Total (Fixed quota) 100
    22. 22. 4. Snowball 4. Snowball Get sampled people to nominate others Researcher collects data on the few members of the target population he or she can locate, then asks those individuals to provide information needed to locate other members of that population whom they know.
    23. 23. Sampling Errors A. Size: sample size should be large as possible depends upon feasibility (time, person, importance of data) B. subject variation: Sometimes observation may be changed on different times (B.P at different times of a day) C. Observer Variation: When 2 or more persons observe same data (No same value) E.g:- Taking Blood Pressure reading D. Technical Fault: By Instrument E. Incomplete Coverage: If 10 out of 100 are non cooperative (i,e 90 or 10 Non co operative)
    24. 24. THANKYOU
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