Z-Table Reference
Find probabilities for Z-scores in the standard normal distribution
What is a Z-Table?
A Z-table, also known as a standard normal table, is a mathematical tool that shows the probability of a standard normal random variable falling below a certain z-score. It's essential for:
- Finding specific probabilities in a normal distribution
- Converting between z-scores and probabilities
- Making statistical inferences about normally distributed data
- Calculating confidence intervals and p-values
Why Use a Z-Table?
Standardization
Convert any normal distribution to a standard form, making comparisons possible across different datasets.
Probability Analysis
Determine the likelihood of observations falling within specific ranges of a normal distribution.
Statistical Testing
Essential for hypothesis testing, confidence intervals, and other statistical procedures.
How to Use the Z-Table
- Find the row (Z) corresponding to the first two digits of your Z-score
- Move across to the column (.00 to .09) for the third decimal place
- The intersection shows the area to the left of that Z-score
- For negative Z-scores, use the absolute value and adjust accordingly
Common Z-Score Values
Z = ±1.96
Used for 95% confidence intervals. 95% of the data falls within 1.96 standard deviations of the mean.
Z = ±2.58
Used for 99% confidence intervals. 99% of the data falls within 2.58 standard deviations of the mean.