Sampling Flashcards
The act of studying or examining only a segment of the population to represent the whole
• Advantages:
− Cheaper
− Faster
− Better quality of information
− Only possible method for destructive procedures (ex: blood count)
SAMPLING
– entire group of individuals or items of interest in the study (eg. Philippines)
Population
– group from which representative information is desired and to which inferences will be made (eg. Metro Manila sa Philippines)
Target Population
– population from which a sample will actually be taken (eg. Makati City sa Metro Manila sa Philippines)
Sampling Population
– units which are chosen in selecting a sample (eg. Mga nakatira sa baranggay 1 sa Makati City sa Metro Manila sa Phil.)
Sampling Unit
_________________ – object or person on whom a measurement if actually taken or an observation is made (eg. tao sa baranggay)
Elementary Unit or Element
_____________________ – a collection of all sampling units / a listing of all units available (eg. record, list sa infirmary, census)
Sampling Frame
Incidence of Leptospirosis in a Tertiary Hospital in Manila
Target Population:
Sampling Population:
Sampling Frame:
Target Population: Residents of Manila
Sampling Population: Manila residents consulting in a tertiary hospital
Sampling Frame: ER census of the tertiary hospital/Admitting office
Prevalence of Obesity among Call Center Agents of Convergys Target Population:
Sampling Population:
Sampling Frame:
Target Population:Call Center Agents
Sampling Population: Call center agents of Convergys
Sampling Frame: List of call center agents working for Convergys
or
Target Population: Call Center Agents of Convergys
Sampling Population: Call center agents of Convergys na Night shift, or call center na inbound or outbound.
Sampling Frame: List of call center agents working for Convergys sa HR.
Rate of Sexually-‐transmitted Infection among CSW’s Olongapo Target Population:
Sampling Population:
Sampling Frame:
Target Population: CSW’s of Olongapo
Sampling Population: CSW’s working in a high-‐end bar
Sampling Frame: List of registered CSW’s
Prevalence of disability among 6-‐12 year old children in a community
Target Population:
Sampling Population:
Sampling Frame:
Target Population: 6 – 12 year old children
Sampling Population: 6 -‐12 year old pupils
Sampling Frame: List of pupils
Target Population: Children in a community
Sampling Population: 6 -‐12 year old children na nasa community
Sampling Frame: Barangay Census
or
Target Population: 6 – 12 year old children
Sampling Population: 6 -‐12 year old children from homes in a rural town
Sampling Frame: List of barangays
Sampling Units: Barangays selected by systematic
sampling Elements: All children aged 6-‐12 yrs from the homes located in the barangays sampled
• The difference between the value of the parameter being investigated vs. the estimate of this value based on the different samples
SAMPLING ERROR
- Sample should be representative / reflect the characteristics and variability of the population
- Sample size should be adequate
- Practicality and feasibility of the procedure
- Economy and efficiency of the design
GOOD SAMPLING DESIGN
BASIC SAMPLING DESIGN
A.** Non-‐probability Sampling Designs** − The probability of each member of the population being selected as part of the sample cannot be determined
B. Probability Sampling Designs − Each member of the population has a known non-‐zero chance of being selected as a sample
− The probability of each member of the population being selected as part of the sample cannot be determined
A. Non-‐probability Sampling Designs
− Each member of the population has a known non-‐zero chance of being selected as a sample
B. Probability Sampling Designs
• **Advantages: **
− Easier to execute
− Sometimes the only possible means
• Disadvantages: − More likely to produce a biased result − Cannot compute reliable estimates
A. NON-‐PROBABILITY SAMPLING DESIGN
What are the types of nonprobabilty sampling design?
- judgmental or purposive
- Accidental or haphazrd
- Quota sampling
- Snowball technique
- Convenience sampling
o a ‘representative’ sample of the population is selected based on an expert’s subjective judgment or some pre-‐specified criteria (ex: infants with autism)
Judgmental or Purposive
o The sample is made up of those who is available (ambush interview)
Accidental or Haphazard
o Samples of a fixed size (quota) are obtained from pre-‐ determined subdivisions of the population (e.g. religion research) o Eg. Perspective sa Holy Trinity ng Iglesia Ni Cristo members; Igorots sa perspective sa isang intervention
Quota Sampling
o The sample is obtained by a process whereby an individual to be included is identified by a member who was previously included (e.g ; CSW, drug users) o Irerefer lang. (eg. HIV, Sex worker, erectile dysfunction)
Snowball technique
o Study units who are easily accessible are selected as samples (e.g. clinical studies)
o Kung sino lang ung dumating/ pagpapalista/
- Convenience Sampling
Safe Sex: Knowledge, Attitudes and Perceptions of HIV positives in the Philippines -‐
SNOWBALL
Acceptability of a Detergent Bar X Among Shoppers in a Supermarket -‐
CONVENIENCE OR HAPHAZARD (better choice)
A Focused Group Discussion on the Impact of Beauty Products in the Self-‐Esteem of Teenagers –
QUOTA
Effect of Monoclonal Antibody (Drug X) in the QOL among Psoriasis Patients of Dermatology OPD
CONVENIENCE (better choice) or PURPOSIVE
Family Planning Method: Preference among Doctors-‐to-‐the-‐Barrios
PURPOSIVE OR QUOTA (better choice)
What are the types of probabality sampliing design?
- Simple random
2, Systemic Sampling
- Stratified Random Sampling
- Cluster Sampling
- multi-stage sampling design
− Most basic type of design. Every element in the population has an equal chance of being included in the sample
− Make a sampling frame: a numbered list of all units in the population from which you want to draw a sample
− Lottery method or use random numbers to select elements − Eg. toss coin, generation or random numbers
- Simple Random Sampling
− Samples are chosen at regular intervals (e.g. every fourth) from a sampling frame
− Researcher must compute for the sampling interval (k=N/n) − Easier to perform than SRS
. Sometimes result in a more representative sample
− Example.
− 70 – isang classroom (N = total population) 10
– kung ilan ang kelangan(n) 70/10 = 7 ang interval kung ang interval ay 7, ang kasali ay 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17…….
- Systematic Sampling
− Population is first divided into non-‐overlapping groups called strata (stratum). SRS is done for each stratum
− Ensures that groups are adequately represented.
Estimates for each stratum may be obtained. Produces reliable results
− Eg. Population: College of Medicine Strata: Year Level, Gender. Population: For Offices Strata: Position, either Blue collar or white collar
- Stratified Random Sampling
− The selection of groups of study units (clusters) instead of the selection of individual study units
− Eg. City – and cluster nyan ay barangay 1 or barangay 2, ung barangay na pipiliin, kasama lahat.
- Cluster Sampling
______________− Combination of sampling designs may be used. − Primary and secondary sampling
- Multi-‐stage Sampling Design
