A score of how a person compares to average in a population. It is used to compare different characteristics, for example, their BMI or their height.

A Z-score shows how a person compares to the average in a population, for different characteristics such as their BMI or height. A Z-score of 0 means the person has an average result. Above 0 means the person’s result is above the average, while a score below 0 means the result is below the average.

For example:
• John is a 30-year-old man with cystic fibrosis. His height Z-score is -1.3. This means he is shorter than the average 30-year-old man.
• Sarah is a 10-year-old girl with cystic fibrosis. Her height Z-score is 0.01, which means she is of average height.

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