Equations · Probability and statistics
z-score
How many standard deviations a value lies above or below the mean.
z = (x − μ) / σ
Aethel says
z equals the quantity x minus mu, over sigma
What it says
Subtract the mean and divide by the standard deviation. A z-score of 2 means two standard deviations above the mean; −1 means one below.
Z-scores put measurements on a common scale, so values from different tests or units can be compared, and they are the input to normal-distribution tables.
Symbol by symbol
| Symbol | Say it | Means |
|---|---|---|
| z | z | the standardised score |
| x | x | the value |
| μ | mu | the mean |
| σ | sigma | the standard deviation |
Where you meet it
Statistics courses, standardised testing and anomaly detection.
Questions
How do you say z-score out loud?
z = (x − μ) / σ is read: “z equals the quantity x minus mu, over sigma.” That is exactly what Aethel says when it meets the formula in a book.
What does z mean in z-score?
z (said “z”) is the standardised score.
What does x mean in z-score?
x (said “x”) is the value.
Can I listen to the equations in my own textbook like this?
Yes. Upload a PDF, EPUB or text file and Aethel reads it aloud with every equation spoken as maths, the way it reads this one, and highlights each sentence as it goes. You can start free.