Z-scores
A standardized value representing how many standard deviations a value is from the mean. For X ~ N(μ, σ²), the z-score is Z = (X - μ) / σ, and Z ~ N(0, 1).
Real World
NFL scouts use z-scores to compare players across positions: a wide receiver running the 40-yard dash in 4.3 seconds has z = −2.1 (very fast) even though that raw time means nothing without knowing the position average.
Exam Focus
A negative z-score is valid — never discard it; state whether the value is above or below the mean to gain interpretation marks.
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