Ztabell

ztabell, commonly called the Z-table or Z-tabell in several languages, is a tabulated resource of the standard normal distribution. It provides the cumulative probability Φ(z) = P(Z ≤ z) for values of z in the standard normal distribution. It is used to translate a z-score into a probability or to determine critical values in hypothesis testing and confidence interval construction.

Format and interpretation: The common version is a two-dimensional grid where rows represent the integer and first decimal places of z and columns represent the second decimal place. The cell value gives the probability that a standard normal variable is less than or equal to z. Some tables present upper-tail probabilities, reverse that, or provide both forms with guidance on symmetry.

Usage and relevance: While modern statistics rely on calculators and software to compute probabilities, the Z-table remains a foundational educational tool and is included in many statistics curricula and exams. Its accuracy depends on the table range and decimal precision; for z-values far in the tails the table may be limited, requiring interpolation or digital computation.

See also: standard normal distribution, Z-score, p-value.