What does a z-score of 0 mean?

A z-score of 0 means the value equals the mean. Negative z-scores indicate values below the mean, positive z-scores indicate values above the mean.

What does a percentile tell me?

A percentile tells you what percentage of values in a normal distribution fall below your observed value. For example, a 84th percentile means 84% of values are below yours.

How do I use z-scores for hypothesis testing?

Compare the p-value to your significance level (typically 0.05). If p-value < 0.05, the result is statistically significant. Use one-tailed for directional tests, two-tailed for non-directional.

What is the 68-95-99.7 rule?

In a normal distribution: ~68% of values fall within 1 standard deviation, ~95% within 2 standard deviations, and ~99.7% within 3 standard deviations of the mean.

What is the difference between one-tailed and two-tailed p-values?

One-tailed p-values test if a value is extreme in one specific direction. Two-tailed p-values test if a value is extreme in either direction and are generally more conservative.

Z-Score Calculator

Gratis z-score calculator. Find the standardized score, percentile rank, one-tailed and two-tailed p-values for hypothesis testing and statistical analysis.

Bereken z-scores, percentiles, and p-values to standardize and interpret data relative to a normal distribution.

z = \frac{x - μ}{σ}

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