Sampling Methods
This sampling method gives every individual in the population an equal chance of being selected.
What is a simple random sample?
Surveying people who are easiest to reach is called this type of sampling.
What is convenience sampling?
In this design, all subjects are randomly assigned to treatments.
What is a completely randomized design?
This principle involves assigning subjects to treatments by chance.
What is random assignment?
Blocking is used to reduce variability caused by this.
What are confounding variables or lurking variables?
A researcher selects every 10th student from a school roster.
What is a systematic sample?
A survey posted online where people choose to respond is an example of this.
What is voluntary response sampling?
Subjects are paired based on similarities, and treatments are randomly assigned within pairs.
What is a matched pairs design?
This principle ensures that there is a group to compare results against.
What is comparison?
If gender may affect results, subjects should be grouped by gender before assigning treatments. This is called:
What is blocking?
The population is divided into groups (like grade levels), and random samples are taken from each group.
hat is a stratified sample?
This type of bias occurs when certain groups are left out of the sampling process.
What is undercoverage bias?
Subjects are divided into groups (blocks) based on a characteristic, then randomly assigned treatments within each block.
What is a randomized block design?
This principle involves keeping other variables constant.
What is control?
Why is blocking useful in an experiment?
It reduces variability and allows more precise comparisons between treatments.
Entire groups (like classrooms) are randomly selected, and all individuals in those groups are surveyed.
What is a cluster sample?
People lie or give inaccurate answers due to the question wording or interviewer.
What is response bias?
Give an example of when a matched pairs design would be more appropriate than a completely randomized design.
When comparing before/after results on the same subjects or using twins/matched individuals.
This principle means using enough subjects to reduce variability and improve reliability.
What is replication?
A study groups students by math ability before assigning teaching methods. What type of design is this?
What is a randomized block design?
Explain one key difference between a stratified sample and a cluster sample.
Stratified samples take some individuals from all groups, while cluster samples take all individuals from selected groups.
A survey is mailed out, but many people do not return it. Identify the bias and explain why it is a problem.
What is non-response bias? It’s a problem because those who don’t respond may differ significantly from those who do.
Explain the key difference between a matched pairs design and a randomized block design.
Matched pairs use pairs (or the same subject twice), while randomized block designs use larger groups (blocks) based on shared characteristics.
Explain why all four principles (control, comparison, random assignment, replication) are necessary for a strong experiment.
They reduce bias, allow cause-and-effect conclusions, ensure fairness in treatment assignment, and improve reliability of results.
Describe a situation where blocking would significantly improve an experiment and explain why.
Example: Testing a drug by age groups—age affects response, so blocking reduces variability and isolates treatment effects.