CRO Glossary
Above-the-Fold Contrast Ratio
The luminance/color difference between key above-the-fold elements and their background, measured to ensure legibility and visual prominence.
Contrast ratio is a numeric measure (commonly expressed as a ratio like 4.5:1) of how distinguishable a foreground element — text, a button, an icon — is from the background behind it. In CRO work, it's most often discussed in the context of the first screen a visitor sees, because that's where attention is scarcest and the cost of a hard-to-read headline or invisible CTA is highest.
Low contrast in this zone is a frequent, quiet conversion killer: a call-to-action button that blends into a hero image, or body copy in light gray on white, can suppress clicks without ever showing up as an obvious 'bug.' Accessibility guidelines (WCAG) set minimum thresholds — typically 4.5:1 for normal text and 3:1 for large text — and these thresholds double as useful conversion heuristics even for users without visual impairments, since low contrast increases cognitive load for everyone under real-world conditions like glare, small phone screens, or distracted skimming.
A concrete example: a SaaS landing page tests a teal 'Start Free Trial' button (contrast ratio 2.1:1 against its background) against the same button in a darker teal (4.8:1). The higher-contrast version often wins not because of color preference but because more visitors actually register that a clickable button exists.
Contrast ratio is measurable with automated tools, which makes it an easy first audit item before investing in more elaborate above-the-fold experiments — fixing a glaring contrast failure sometimes yields a bigger lift than a full redesign.
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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