Introduction to Planning a Study - AP Statistics
- Identify the main goal of an observational study.
- The main goal is to describe or compare existing groups without interference. No treatments are imposed; researchers simply observe.
- What is an observational unit?
- An observational unit is the entity on which measurements are made. The individual item or person being measured.
- Define a sample in the context of statistical studies.
- A sample is a subset of individuals chosen from a population to represent it. Smaller group used to make inferences about the population.
- What does a simple random sample (SRS) mean?
- An SRS is a sample where each set of n individuals has an equal chance of selection. Ensures every possible sample has equal probability of selection.
- Explain why blinding is used in experiments.
- Blinding prevents bias by ensuring participants or researchers are unaware of group assignments. Reduces expectation effects that could skew results.
- What is a controlled experiment?
- A controlled experiment involves manipulating one variable to determine its effect. Researchers actively impose treatments to observe effects.
- Define confounding variable.
- A confounding variable is an outside influence that affects the dependent and independent variables. Can make it impossible to determine true cause-effect relationships.
- What is the purpose of a pilot study?
- A pilot study tests the feasibility of a larger study. Identifies potential problems before full-scale study.
- What is a parameter in statistical terms?
- A parameter is a numerical summary of a population. Describes a characteristic of the entire population.
- How does a convenience sample differ from a random sample?
- A convenience sample is chosen based on ease of access, not random selection. Convenience ignores randomness, creating potential bias.
- Define a lurking variable.
- A lurking variable is not included as an explanatory or response variable but affects interpretation. Hidden variable that can confound study results.
- What is a matched pairs design?
- A matched pairs design involves pairing similar units and randomly assigning treatments. Controls for differences between subjects more effectively.
- What is the role of replication in experiments?
- Replication ensures that results are consistent and not due to chance. Multiple trials help distinguish real effects from random variation.
- What is the definition of a response variable?
- A response variable is the outcome of interest measured in a study. What researchers want to predict or explain.
- What type of study is best for determining causality?
- An experiment is best for determining causality. Only experiments can establish cause-and-effect relationships.
- What is systematic sampling?
- Systematic sampling involves selecting every k-th individual from a list. Simple method but can introduce bias if pattern exists.
- What does 'double-blind' mean in an experimental context?
- Neither the participants nor the researchers know who receives the treatment. Prevents expectation bias from both subjects and researchers.
- Identify the main purpose of random sampling.
- Random sampling ensures each member of the population has an equal chance of selection. Prevents selection bias and enables valid statistical inference.
- What is an experimental unit?
- An experimental unit is the smallest unit to which a treatment is applied. The individual subject that receives one treatment condition.
- What is the main objective of a census?
- To gather data from every member of the population. Provides complete information but is often impractical.
- What are the two main types of bias in sampling?
- Selection bias and response bias. Two major sources that can invalidate study results.
- What is cluster sampling?
- Cluster sampling involves dividing the population into clusters and randomly selecting clusters to sample. Useful when population is naturally grouped geographically.
- Define the placebo effect.
- The placebo effect is a beneficial response to a placebo treatment. Shows power of psychological factors in perceived improvement.
- What does 'response bias' refer to?
- Response bias occurs when participants provide inaccurate answers due to wording or interviewer influence. Question design or interviewer presence affects truthful responses.
- Identify one potential issue with convenience sampling.
- It can lead to biased results as it may not represent the entire population. May not represent the target population accurately.
- What is a sampling frame?
- A sampling frame is the list or database from which a sample is drawn. The actual list used to select sample members.
- What is the Hawthorne effect?
- The Hawthorne effect is a change in behavior due to awareness of being observed. Being studied can change natural behavior patterns.
- Define a statistic in the context of statistical studies.
- A statistic is a numerical summary of a sample. Describes a characteristic calculated from sample data.
- What is the definition of a population in statistics?
- A population is the entire group of individuals or instances about which we seek information. This is the complete group being studied.
- What is the significance of control groups?
- Control groups provide a baseline to compare the effects of treatments. Allow comparison to measure treatment effectiveness.
- Define bias in the context of statistical studies.
- Bias is a systematic error that results in an incorrect estimate of an effect. Creates consistently wrong results in a particular direction.
- Define explanatory variable.
- An explanatory variable is a factor that is manipulated to determine its effect. The variable researchers think causes changes in response.
- Identify the purpose of a placebo in experiments.
- A placebo is used to test the efficacy of a treatment by comparing it with a control group. Controls for psychological effects of receiving treatment.
- What is the key characteristic of a voluntary response sample?
- Participants choose themselves to be part of the sample, which can cause bias. Creates strong selection bias toward motivated individuals.
- What is the purpose of randomization in an experiment?
- Randomization helps eliminate bias and balance known and unknown confounding variables. Creates comparable groups by distributing confounding variables evenly.
- Define non-response bias.
- Non-response bias occurs when selected participants do not respond. Missing responses may differ systematically from those received.
- How does blocking work in experimental design?
- Blocking involves grouping similar experimental units and randomizing within blocks. Reduces variability by controlling for known confounding factors.
- How is a stratified random sample obtained?
- Divide the population into strata and take an SRS from each stratum. Ensures representation from each important subgroup.
- Differentiate between observational study and experiment.
- In an observational study, variables are not manipulated; in an experiment, they are. Key difference is whether treatments are imposed.
- Identify one advantage of stratified sampling.
- It increases precision by ensuring representation from each stratum. Reduces variability by controlling for known differences.