Common Misreads of Performance Data (and How to Avoid Them)
Purpose
List common mistakes when interpreting performance data, and how to avoid them when measuring Speed Layer.
Misread 1: Treating one lab score as the truth
Avoid using a single PageSpeed run as a success metric. Use trends and real user experience data.
Misread 2: Looking only at averages
Averages can hide poor experiences for a large group of users. Percentiles such as p75 are often more meaningful.
Misread 3: Mixing page types
Homepage, SRP, and VDP behave differently. Track them separately.
Misread 4: Ignoring device differences
Mobile performance often differs dramatically from desktop. Segment results.
Misread 5: Attributing improvements to the wrong change
Performance can change due to:
- New third party tags
- Platform releases
- CDN or hosting changes
Track changes over time and isolate tests when possible.
Misread 6: Treating faster as better even when functionality breaks
A site is not successful if key tools fail. Validate lead tools and shopping flows alongside performance.
Related pages
- Setting Baselines and Comparing Before/After
- Reading Trends vs One-Time Scores
- Ensuring Critical Tools Still Load Properly