ETC Exam Sampling Types and Errors

Convenience Sampling. What is it? What are the pros and cons?

Selecting individuals who are easiest to access.

Pros: Quick, easy and inexpensive

Cons: High risk of bias, not representative

Simple Random Sampling. What is it? What are the pros and cons?

Each individual in the population has an equal chance of being selected.

Pros: Minimises selection bias, easy to analyse

Cons: Can be impractical for large/dispersed populations

Systematic Sampling. What is it? What are the pros and cons?

Selecting every nth individual from a list.

Pros: Simple to implement, evenly spread

Cons: May introduce bias if there’s a hidden pattern in the population

Cluster Sampling. What is it? What are the pros and cons?

Dividing the population into clusters, randomly selecting clusters, then sampling all or some with them.

Pros: Cost effective, useful for large populations

Cons: Higher sampling error if clusters are not homgenous

Stratified Sampling. What is it? What are the pros and cons?

Dividing populations into subgroups(strata) and then sampling from each.

Pros: Ensure representation of key subgroups

Cons: Requires knowledge of population structure and strata

Sampling Bias. What is it?

Some members of the target population are less likely to be included than others.

Attrition bias. What is it?

Participants who drop out of a study are different from those who remain

Volunteer Bias. What is it?

Participants who choose to participate in studies are generally different to those who don not.

Survivorship Bias. What is it?

Successful observations are more likely to be represented than unsuccessful ones.

Non-response bias. What is it?

Participants who refuse to participate/drop out of a study may be different from those who take part.

Undercoverage biad. What is it?

Participants who are inadequately represented.