Chapter 19 - Population Sampling Flashcards
What is a population?
A group or subgroup of individuals, communities or organizations
Name and define the 4 types of a population
- Target population - the broadest, broad population to which the results of the study should be applicable
- Source population - A well-defined subset of individuals from the target population from which potential study participants will be sampled
- Sample population - consists of individuals asked to participate in the study
- Study population - consists of people eligible to participate in the study
What is Sampling bias vs. Non-sampling bias?
- Sampling bias (or ascertainment bias) occurs when the individuals sampled for a study systematically are not representative of the source population.
- Nonrandom-sampling bias occurs when each individual in the source population does not have an equal chance of being selected for the sample population.
What methods are used to ensure that the sample population is representative of the source population?
Probability-based sampling methods
List and define the 4 examples of types of probability-based sampling
1) Simple random sampling:
Every person in the population has an equal chance of being selected in a study
2) Systematic sampling:
For larger populations, we might not want every other individual, so every nth person is selected
3) Stratified random sampling:
Populations and groups are first divided and grouped based on a characteristic before selection takes place
4) Clustered sampling:
When a sample is divided into clusters, typically based on natural-occurring groups
What is a convenience population?
A non probability-based source population selected due to ease of access to those individuals, schools, workplaces, organizations, or communities (i.e. for convenience)
Why does convenience sampling have to be done with caution?
Because convenient samples can often be systematically different from the target and source populations they are intended to represent
List and explain the two different types of Convenient sampling.
1) Chain/snowball/referral sampling: Encouraging people who took the survey to send it to others
2) Respondent-driven sampling: Combines “Snowball sampling” with a mathematical model that weighs the sample to compensate for the fact that the sample was collected in a non-random way
What is the participation rate?
The percentage of members of a sample population who are included in the study population.
What is selection bias? What helps prevent selection bias?
a) A form of bias that occurs when the members of the study population are not representative of the source population from which they were drawn
b) A high participation rate helps prevent it
What is a population-based study?
A population-based study is a study that uses a random sampling method to generate a sample population that is representative of a well-defined larger population.
What is a census?
a census is a complete enumeration of a population, such as a count of every resident of a country, the number of inpatients at a particular hospital at noon on a selected day, or the number of employees of a large company.
Why are convenience populations not suitable for most cross sectional studies?
Because they are not population-based?
What is a nested-case control study?
A variation of a case–control study in which cases and controls are drawn from the population in a fully enumerated cohort
What does a nested-case control study minimize?
It minimizes recall bias because data about past exposures were collected at the time of the exposure and are not based on what the participants remember
Define Berkson’s bias, Healthy worker bias and Exclusion bias.
Berkson’s bias - occurs when cases and controls are pulled from hospitals and are more likely than the general population to get more diseases and conditions happening at once
Healthy worker bias - When you only pull from people who are working and therefore they are systematically healthier individuals
Exclusion bias - When different eligibility criteria are applied to individuals being pulled (cases and controls) such as when controls (people who do not usually have health conditions) with health conditions related to an exposure are excluded but cases (people who do) with those comorbidities are not excluded.
What is eligibility criteria?
Eligibility criteria, also known as inclusion and exclusion criteria, are the characteristics that determine which participants can and cannot take part in a study
Fill in the blank:
Qualitative data collection is not a ________ process based on ______ of individuals
Qualitative data collection is not a detached, structured process based on a random sample of individuals.
What are Key informants?
Individuals selected to participate in a qualitative study because they have expertise relevant to the study question
What is Purposive sampling?
A non probability-based sampling method that recruits participants for a qualitative study based on the special insights they can provide.
What is data saturation?
A time in the research process in which no new information about a particular theory is emerging from additional data collection because variations across population members have already been captured
a) What are Vulnerable
b) populations? List some examples.
a) Populations whose members might have limited ability to make an autonomous decision about volunteering to participate in a research study.
b) young children, people with cognitive disabilities, people in prison, socially marginalized populations
What is Community-based participatory research (CBPR)?
When members of the community work together, determine the priorities for the research project and take part in every stage of the process
