szignifikanciaszint

Szignifikanciaszint, or significance level, is a concept in hypothesis testing that sets the threshold for deciding whether an observed effect is statistically significant. It is the pre-specified probability, under the null hypothesis being true, of rejecting the null hypothesis when there is no real effect. This probability is denoted by alpha (α) and is chosen before data are collected.

In practice, if the observed p-value from the test is less than or equal to α, researchers reject the null hypothesis; if the p-value is greater than α, they fail to reject it. The significance level thus controls the risk of a Type I error, the error of concluding that there is an effect when none exists. Common choices for α are 0.05, 0.01, and 0.10, with the selection reflecting field conventions and the consequences of false positives.

The choice of α also influences statistical power—the probability of correctly detecting a true effect. Lowering α reduces the chance of a Type I error but typically requires larger sample sizes to achieve the same power. For two-sided tests, the significance level is distributed across both tails of the sampling distribution (e.g., α = 0.05 corresponds to 2.5% in each tail), whereas one-sided tests place the entire α in a single tail.

Significance level is related to, but distinct from, confidence intervals: a two-sided test at α corresponds to constructing a (1−α) confidence interval. When multiple tests are performed, adjustments (such as Bonferroni or Holm corrections) may be applied to control the overall error rate. The szignifikanciaszint is a pre-specified criterion, not a measure of the effect size or the probability that H0 is true given the data.