Sampling
What is a simple random sample (SRS)?
A sample in which every group of the same size has an equal chance of being selected
What is voluntary response bias?
Bias introduced when people choose whether to respond, usually with strong opinions.
What is an observational study?
A study where researchers only observe and do not impose treatments.
What are the 3 principles of experimental design?
Control, randomization, replication.
Define “population.”
The entire group you want information about.
What is a systematic sample?
A sample drawn by selecting every nth person from a list or order.
How can undercoverage affect a sample?
Some groups in the population are left out or underrepresented.
What defines an experiment?
A study where researchers actively impose treatments to measure responses.
What does it mean to randomly assign treatments?
Each subject has an equal chance of receiving any treatment.
What is a sample?
A subset of the population used to draw conclusions.
Why might convenience sampling lead to inaccurate results?
It may cause undercoverage and is unlikely to represent the full population.
What is nonresponse bias?
When a selected individual doesn’t respond and differs from those who do.
What is the explanatory variable in an experiment?
The variable being manipulated to observe its effect.
What is the purpose of a control group?
To serve as a baseline for comparison.
Define “confounding variable.
A variable associated with both the explanatory and response variables.
What is stratified sampling?
The population is divided into groups (strata), and an SRS is taken from each group.
How can question wording introduce bias?
Leading or emotionally charged wording can influence responses.
Why are experiments better than observational studies for determining cause and effect?
They control confounding variables and randomly assign treatments.
How does blocking improve an experiment?
It reduces variability by grouping similar subjects.
What is a response variable?
The outcome measured in a study.
What’s the difference between stratified and cluster sampling?
Stratified selects some individuals from all groups; cluster selects all individuals from some groups.
Give an example of response bias.
A person lying on a survey due to social pressure or embarrassment.
A researcher compares test scores of students who sleep 6 hours vs. 8 hours without assigning sleep schedules. What kind of study is this?
Observational – no treatment imposed.
What is a matched pairs design?
Subjects are paired based on similarities, and each receives both treatments or one from each pair receives one treatment.
Define “sampling frame.”
The list from which the sample is actually drawn.