Introduction to Planning a Study - AP Statistics

Blinding prevents bias by ensuring participants or researchers are unaware of group assignments. Reduces expectation effects that could skew results.

It can lead to biased results as it may not represent the entire population. May not represent the target population accurately.

Participants choose themselves to be part of the sample, which can cause bias. Creates strong selection bias toward motivated individuals.

Response bias occurs when participants provide inaccurate answers due to wording or interviewer influence. Question design or interviewer presence affects truthful responses.

Non-response bias occurs when selected participants do not respond. Missing responses may differ systematically from those received.

An experimental unit is the smallest unit to which a treatment is applied. The individual subject that receives one treatment condition.

Random sampling ensures each member of the population has an equal chance of selection. Prevents selection bias and enables valid statistical inference.

A convenience sample is chosen based on ease of access, not random selection. Convenience ignores randomness, creating potential bias.

The placebo effect is a beneficial response to a placebo treatment. Shows power of psychological factors in perceived improvement.

Selection bias and response bias. Two major sources that can invalidate study results.

An observational unit is the entity on which measurements are made. The individual item or person being measured.

An experiment is best for determining causality. Only experiments can establish cause-and-effect relationships.

A sampling frame is the list or database from which a sample is drawn. The actual list used to select sample members.

A response variable is the outcome of interest measured in a study. What researchers want to predict or explain.

A statistic is a numerical summary of a sample. Describes a characteristic calculated from sample data.

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.

The main goal is to describe or compare existing groups without interference. No treatments are imposed; researchers simply observe.

A controlled experiment involves manipulating one variable to determine its effect. Researchers actively impose treatments to observe effects.

Bias is a systematic error that results in an incorrect estimate of an effect. Creates consistently wrong results in a particular direction.

Divide the population into strata and take an SRS from each stratum. Ensures representation from each important subgroup.

Randomization helps eliminate bias and balance known and unknown confounding variables. Creates comparable groups by distributing confounding variables evenly.

A confounding variable is an outside influence that affects the dependent and independent variables. Can make it impossible to determine true cause-effect relationships.

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.

Neither the participants nor the researchers know who receives the treatment. Prevents expectation bias from both subjects and researchers.

To gather data from every member of the population. Provides complete information but is often impractical.

In an observational study, variables are not manipulated; in an experiment, they are. Key difference is whether treatments are imposed.

An explanatory variable is a factor that is manipulated to determine its effect. The variable researchers think causes changes in response.

Systematic sampling involves selecting every k-th individual from a list. Simple method but can introduce bias if pattern exists.

It increases precision by ensuring representation from each stratum. Reduces variability by controlling for known differences.