Question 1

Can a z-score be negative?

Accepted Answer

Yes. A negative z means the value is below the mean; z = −1.5 is 1.5 SD below average.

Question 2

What is a good z-score?

Accepted Answer

There is no universal good value; it depends on whether higher is better. It only tells you position relative to the mean.

Question 3

How do I turn a z-score back into a raw value?

Accepted Answer

Use x = μ + z × σ. For z = 2, μ = 100, σ = 15, x = 130.

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