W2 S16 Flashcards
Target population
people you want your results to apply to
ex, everyone in Canada
Source population or Sampling frame
People from whom the population is selected
-population where your study subjects are drawn
ex, everyone on Canadian Electrical role
Sample
people approached to take part in the survey
ex, random sample of those listed
Study population
people who actually took part in the survey
ex, those who agree to take part
What is Probability Sampling?
It involves using selection techniques wherein the probability of each sampling unit is know
What are the 5 methods of Probability sampling?
- Simple random sampling
-ex, picking out of hat - Systemic Sampling
-ex, picking every 3rd person - Stratified random sampling:
-ex, random sampling from distinct groups
4.Cluster sampling:
-ex,(natural clusters rather than individual units are selected - Multistage sampling:
ex,( primary sample units are selected
- Simple random sampling:
- number population and randomly choose numbers that come out of random number generator
-ex, picking number out of hat
- Systematic Sampling
-usually, a random start
-the ORDER of population in the sample frame should be RANDOM (not by age or cities for example)
- Stratified Sampling
Random samples from distinct groups
–geography (urban, rural, suburban
–sex (male, female, other)
4.Cluster Sampling
-Natural clusters (schools, neighbourhoods) rather than individual units are selected
-observation are made on ALL units within a cluster
-cluster sampling of schools
—-all eligable children within each school included
1) Four out of 10 clusters are randomly selected
2) All within the selected clusters are recruited
- Multistage Sampling
- primary sampling units are selected (e.g) municipalities)
-secondary units selected within primary units (e.g. individuals)
-may have more levels
—–secondary units: city blocks
—–tertiary units: individuals
1) Five out of 10 clusters are randomly selected
2) within the selected clusters participated are (again) randomly sampled
Non-probability sample
Convenience Sample:
Selection from A non-probability based source population due to ease of access to those individuals, schools, workplaces, organizations, or communities
-use with caution
-often systematically different from the target and source populations they are intended to represent
Non-probability sample
Purposive sampling:
(think of purple)
- recruitment of the participants for a QUALITATIVE study based on the special insights they can provide
Key informants
are individuals selected to participate in a qualitative study because they have expertise relevant to the study questions
What are the errors associated with sampling?
-does the sample represent the ____ population?
External validity -
Sampling bias-
selection bias-
- does the sample represent the target population
- external validity:
the ability of its results to be generalized to the entire population
-sampling bias:
error that systematically skews results in a certain direction.
-Selection bias
is a kind of error that occurs when the researcher decides who is going to be studied.
n
n
Berkson’s bias
can occur when cases and controls for a study are recruited from hospitals and therefore are more likely than the general population to have comorbid conditions
-choose more vulnerable people for study
Health worker bias
can occur when participants are recruited from occupational populations and therefore are systematically healthier than the general population
-choose healthier people for study