Chapter 19 - Population Sampling

Question 1

What is a population?

Answer 1

A group or subgroup of individuals, communities or organizations

Question 2

Name and define the 4 types of a population

Answer 2

1. Target population - the broadest, broad population to which the results of the study should be applicable
2. Source population - A well-defined subset of individuals from the target population from which potential study participants will be sampled
3. Sample population - consists of individuals asked to participate in the study
4. Study population - consists of people eligible to participate in the study

Question 3

What is Sampling bias vs. Non-sampling bias?

Answer 3

• 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.

Question 4

What methods are used to ensure that the sample population is representative of the source population?

Answer 4

Probability-based sampling methods

Question 5

List and define the 4 examples of types of probability-based sampling

Answer 5

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

Question 6

What is a convenience population?

Answer 6

A non probability-based source population selected due to ease of access to those individuals, schools, workplaces, organizations, or communities (i.e. for convenience)

Question 7

Why does convenience sampling have to be done with caution?

Answer 7

Because convenient samples can often be systematically different from the target and source populations they are intended to represent

Question 8

List and explain the two different types of Convenient sampling.

Answer 8

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

Question 9

What is the participation rate?

Answer 9

The percentage of members of a sample population who are included in the study population.

Question 10

What is selection bias? What helps prevent selection bias?

Answer 10

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

Question 11

What is a population-based study?

Answer 11

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.

Question 12

What is a census?

Answer 12

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.

Question 13

Why are convenience populations not suitable for most cross sectional studies?

Answer 13

Because they are not population-based?

Question 14

What is a nested-case control study?

Answer 14

A variation of a case–control study in which cases and controls are drawn from the population in a fully enumerated cohort

Question 15

What does a nested-case control study minimize?

Answer 15

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

Question 16

Define Berkson’s bias, Healthy worker bias and Exclusion bias.

Answer 16

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.

Question 17

What is eligibility criteria?

Answer 17

Eligibility criteria, also known as inclusion and exclusion criteria, are the characteristics that determine which participants can and cannot take part in a study

Question 18

Fill in the blank:
Qualitative data collection is not a ________ process based on ______ of individuals

Answer 18

Qualitative data collection is not a detached, structured process based on a random sample of individuals.

Question 19

What are Key informants?

Answer 19

Individuals selected to participate in a qualitative study because they have expertise relevant to the study question

Question 20

What is Purposive sampling?

Answer 20

A non probability-based sampling method that recruits participants for a qualitative study based on the special insights they can provide.

Question 21

What is data saturation?

Answer 21

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

Question 22

a) What are Vulnerable
b) populations? List some examples.

Answer 22

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

Question 23

What is Community-based participatory research (CBPR)?

Answer 23

When members of the community work together, determine the priorities for the research project and take part in every stage of the process