Sampling And Representativeness Flashcards
What is a population?
Entire group of people of interest
What is a sample?
Subgroup of the population
What is a sampling frame?
The group from which the sample is chosen.
Not always the same as the population of interest
What occurs if the sampling from differs from population of interest?
Under-representation
Describe the sampling process?
Category of interest Population Sampling frame Sample Individual participants
What dose generalisation from a sample to a population depend on?
Representativeness
What two types of bias affects representativeness of a sample ?
Selection bias
Response bias
What is selection bias?
Over representation of segment of population
-occurs from the sampling method based on convenience.
What is response bias?
- problems for questionnaire studies or surveys.
- underrepresentative sample
What is volunteer bias and who was it introduced by?
Rosenthal & Rosnow
- More highly educated and have a higher need for approval
- more social and less authoritarian
- More ‘arousal seeking’
- Females more likely than males
How do you reduce volunteer bias?
- Making appeal for particpants as interesting and non-threatening as possible
- Theoretical and practical importance
- avoiding ‘stressful’ research.
- Request made by an person of status as high as possible and preferably by a woman’.
What is self sampling?
A problem for under representation.
- as people who only see the advert
- interested in doing research or interested in the effects of stress
- free during the day
——will take part in the study
What sampling methods do we have?
Probability sampling:
-random sampling
- Stratified sampling
- Cluster sampling
Non-probability sampling:
-Opportunity/convenience sampling
- purposive sampling
- quota sampling
What is probability sampling?
- uses some form of random selection
- each member of the population has a specific probability of being chosen as a participant
- researcher can Estimate likelihood that sample findings will differ or be similar from population
- High degree of representativeness
What is random probability sampling?
Simple random sampling:
-sample chosen by chance.
What is systematic random sampling?
Sample members from a population are selected at a fixed sampling interval
-sampling interval is calculated:
Population divided by sample size.
-Everyone in the population has an equal chance of selection
Why is a true random sample very difficult to achieve?
-difficult if population is large.
What is stratified sampling?
Population is divided into subgroups/strata
Random sampling within each strata
Divided into subgroups according to variables likely to affect the dependent variable.
What is cluster probability sampling?
Divide population into groups or clusters, then select random sample of clusters
Every member of selected cluster is part of the sample.
-typically used when you cant obtain list of population
What is non probability sampling?
Probability of any member of the population being chosen is unknown and cant be calculated
- convenient and easy
- probably not representative
- Generalisation problems
What three kinds of non-probability sampling do we have?
Opportunity/convenience sampling
Purposive sampling
Quota sampling
What is opportunity/convenience sampling?
Participants for sample are chosen if they are conveniently available at the time.
-this can cause bias in the sample
What is purposive sampling?
Particpants are selected on the basis of belonging to a specific group or having certain experiences.
-selective is not random
What is quota sampling?
Population is divided into subgroups
Participants selected by researcher until quota is reached
-non-random sample as selection is done by researcher
- High potential for bias:
- Friendly looking people
- convenient location
