CRO Glossary
Statistical Noise
Random variation in metrics that isn't caused by the change being tested, which can create misleading test results.
Statistical noise is the natural, random fluctuation in data that happens even when nothing meaningful has changed — different visitors arriving on different days, different devices, different traffic sources, and plain chance. Every A/B test result is a mix of signal (the true effect of your change) and noise, and the entire purpose of significance testing is to estimate how much of what you're seeing could plausibly be explained by noise alone.
Noise is why short tests, low-traffic tests, or tests measured on volatile metrics (like average order value, which can be skewed by a handful of large orders) are so unreliable. It's also the reason A/A tests exist: running a test with no real difference between variants lets teams measure how much natural noise their metrics carry, which sets expectations for how skeptical to be of small observed lifts.
A concrete example: a variant shows a 4% lift in conversion rate after two days. Before celebrating, a careful analyst checks whether that gap falls within the range you'd expect from random noise given the sample size so far — often it does, and the 'lift' disappears with more data.
Related terms
Above vs Below Median Split
A segmentation technique that divides users into two groups at the median of a metric to compare high and low engagers.
Qualitative Feedback Loop
A recurring process of collecting and acting on user comments, session recordings, and survey responses to inform test hypotheses.
Experiment Metadata
The structured record of who, what, when, and how for a test — hypothesis, owner, dates, variants, and metrics used to track and audit it.
Pre-Test Analysis
The upfront work of validating traffic, metrics, and baseline data quality before launching an experiment.
Above-the-Fold vs Below-the-Fold Messaging Hierarchy
How the order and prominence of value-proposition messaging is split between the visible screen and the rest of the page.
Experiment Contamination
When a control or variant group is unintentionally exposed to the other condition, corrupting the comparison.
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