Which of the following statements is true about a z-score?

• A. A z-score is always a positive number.
• B. A z-score is the same as the probability of an event.
• C. A z-score indicates how many standard deviations a data point is from the mean.
• D. A z-score can only be calculated for data sets with a mean of $0$.

Answer: (C)

Verified step by step guidance

1. Understand what a z-score represents: it measures the number of standard deviations a data point is from the mean of the data set.
2. Recall that a z-score can be positive, negative, or zero depending on whether the data point is above, below, or exactly at the mean.
3. Recognize that a z-score is not a probability itself, but it can be used to find probabilities by referring to the standard normal distribution table.
4. Note that a z-score can be calculated for any data set with a known mean and standard deviation; the mean does not have to be zero.
5. Conclude that the true statement is: 'A z-score indicates how many standard deviations a data point is from the mean.'