Data Collection, Bias, and Study Design

SAT Math · Axiom Academy

Data Collection, Bias & Study Design Evaluate study validity and identify sources of bias A random sample is one where every member of the population has an equal chance of being selected. This is the gold standard for collecting unbiased data. To survey student opinions at your school, the school randomly selects 100 students from all 2,000 students using a computer randomizer. Why it's good: Every student has an equal chance of being selected. The sample should represent all grade levels, interests, and backgrounds. Bias occurs when the sample is not representative of the population. The SAT frequently tests your ability to identify sources of bias. Example: Surveying only customers at the mall (excludes those who shop online) Example: Using phone surveys misses people without phones Example: Asking "Do you exercise regularly?" produces biased results—people exaggerate Example: A survey about retirement savings gets responses mostly from wealthy people Example: "Don't you think this school needs better funding?" is leading. Better: "What changes would improve this school?" A mall surveyor asks shoppers: "Do you prefer shopping at this mall?" Only people at the mall can respond. Bias identified: Selection bias. The sample excludes people who prefer other stores or shop online. Observational Studies vs. Experiments These are two fundamentally different ways to gather data, and they have very different limitations.

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