Measures of Center, Spread & Margin of Error
The SAT's Problem Solving and Data Analysis section tests statistical literacy at a sophisticated level. Mean (average) is sensitive to outliers—a single extreme value can dramatically shift it—while the median (middle value when data is ordered) is resistant. Standard deviation measures the spread of data around the mean: a low standard deviation indicates data is tightly clustered; a high one shows it is widely dispersed. The SAT won't ask you to calculate standard deviation by hand, but you must interpret it. If Set A has σ = 2 and Set B has σ = 8, Set B is more variable. Margin of error (MOE) is critical for survey interpretation questions. A poll showing 52% ± 4% means the true value is likely between 48% and 56%—you cannot conclude a definitive winner. The SAT tests whether you understand that larger, randomly selected samples produce smaller margins of error, and that non-random (biased) samples cannot be used to make valid population inferences.