CRO Glossary
Above-the-Fold Image Compression Test
An experiment comparing image file sizes or formats for hero visuals to measure the trade-off between load speed and visual fidelity on conversion.
This is a variant of performance-focused testing where teams compress, resize, or convert hero images (e.g., swapping a large PNG for an optimized WebP file) to see whether faster load times improve conversion rates enough to offset any perceived drop in image quality. Because the hero image is usually the heaviest asset above the fold, it's often the first target when page speed is suspected of hurting conversion.
Practitioners care about this because speed and aesthetics frequently pull in opposite directions: a beautifully art-directed hero shot can add hundreds of milliseconds to load time, and that delay disproportionately affects mobile users on slower connections. Rather than assume compression will help or hurt, teams run a controlled test to quantify the actual impact on metrics like bounce rate, click-through rate, and downstream conversion.
A concrete example: an e-commerce site tests three versions of its homepage hero — the original 2MB JPEG, a compressed 400KB JPEG, and a modern 250KB WebP file — while holding all other elements constant. If the compressed versions load a full second faster and show no statistically significant drop in perceived quality (measured via engagement or survey), the team can adopt the lighter asset sitewide with confidence.
This test is especially relevant for mobile-first experiences and markets with lower average bandwidth, where every extra second of load time can measurably increase abandonment before a visitor even sees the rest of the page.
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.
See this in the wild
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