Null Hypothesis
Also called: H0, alternative hypothesis
The null hypothesis is the default claim a test tries to disprove — usually that there is no effect or no difference. Failing to reject it is not evidence that it's true, only that the data didn't rule it out, a distinction routinely lost in reporting. It must be stated before looking at the data, since a null chosen afterwards guarantees a finding.
Where this is taught
Definitions are the trailer. These free levels turn Null Hypothesis into something you play — one bite-size lesson, with worked examples, a quiz and XP.