Which tool fits which question?
| Question | Starting point | Limit |
|---|---|---|
| How far is a value from the mean? | Z-scores and the normal distribution | Standardising a value does not establish a normal distribution. |
| How can a difference between two means be examined? | t and F tables | The design and assumptions matter. |
| How do event rates in two groups compare? | Absolute and relative risk | Compare the same event over the same period. |
Archived tables and present-day use
The ELYADAL statistical tables document is preserved as a historical source. Check which probability a printed table gives: the left tail, right tail and area between the mean and z are different. Looking up the same number in a different table and obtaining another result may not be a calculation error.
Open the archived statistical tables PDF. Our current web explanations do not present this document as a new edition. The explanations and tools have their own dates.
Include the calculation in your report
State the formula, the units of the inputs, the sample size and the distribution you used. A number without an explanation of how it was calculated is not an account the reader can check. These tools are for learning; they do not automatically select a method for your dataset.
Sources and provenance
Source check / web edition: 14 October 2026. Historical documents retain their own original dates.