Population & Sample

Question 1

What is the target population?

Answer 1

Population which we aim to apply our results to

Question 2

What is the source population?

Answer 2

Sampling frame - list of accessible members of target population

Question 3

What is the eligible population?

Answer 3

Large fraction of the source population will be excluded when study criteria are applied i.e. ineligible

Question 4

Who are study entrants?

Answer 4

When eligible population are approached, large portion will be excluded due to e.g. lack of consent, non-response etc.
Those left are the study entrants

Question 5

Who are the study participants?

Answer 5

Not all the study entrants will complete study requirements or be available for follow-up. The remnants are in this group.

Question 6

What is sampling error?

Answer 6

Difference between outcome value estimated from sample and true-whole population outcome one might get by including everyone in the population

Question 7

What does sampling error depend on?

Answer 7

Sampling technique

Sample size

Question 8

What type of sampling reduces sampling error?

Answer 8

Random sampling

Question 9

What sample sizes produce less sampling error?

Answer 9

Large sample sizes

Question 10

What is non-probability sampling

Answer 10

Non-random sampling

Question 11

Disadvantages of non-random sampling

Answer 11

Generalisability is weaker

Question 12

Types of non-random sampling

Answer 12

Quota
Convenience
Volunteer
Snowball
Consecutive
Purposive

Question 13

What is quota sampling?

Answer 13

Sampling frame divided into subgroups called strata based on selected variables
Non-random sample picked from each stratum

Question 14

What is snowball sampling?

Answer 14

One identified subject helps to locate another subject

Question 15

What is consecutive sampling?

Answer 15

Case series of consecutive patients with conditions of interest

Question 16

What happens in consecutive sampling

Answer 16

All patients who present to research site at time of study are included

Question 17

What types of studies are purposive sampling used in?

Answer 17

Qualitative

Question 18

What happens in purposive sampling?

Answer 18

Subjects picked deliberately based on pre-requisite objectives

Question 19

Types of purposive sampling

Answer 19

Extreme
Critical case
Theoretical purposive

Question 20

What happens in extreme sampling?

Answer 20

Cases representing two extremes are recruited

Question 21

What happens in critical case sampling?

Answer 21

Subjects expected to yield maximum information are selected

Question 22

What happens in theoretical purposive sampling?

Answer 22

Subsequent recruitment depends on those categories that emerged from data so far

Question 23

Another name for systematic sampling

Answer 23

Interval sampling

Question 24

What happens in interval sampling?

Answer 24

Every nth item from sampling frame is selected

Question 25

Difference between random and non-random sampling

Answer 25

In random sampling, each individual in the population has an equal chance of being chosen