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Metrics type: Supporting Metrics • Category: Website Performance

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At a glance

Per-template Mobile vs Desktop score comparison, surfaces the device gap broken out by page type (homepage, PDP, collection, cart, checkout, etc.). Different templates carry different mobile-vs-desktop gap patterns; this card lets the merchant identify which templates need targeted mobile work. Pairs with psi_mobile_vs_desktop_score which gives the site-weighted aggregate; this card decomposes by template.

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Calculation

Calculated automatically from your Website Performance (PageSpeed + CrUX) data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading.

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Worked example

A UK-based BigCommerce fashion store, per-template comparison Wednesday 15 May 26. What the per-template view is telling us:
  1. Collection page has the highest gap × traffic score (8.7). Despite homepage having the largest gap, collection has higher traffic share, making it the highest-leverage optimisation target. Fix collection page first.
  2. The optimisation priority by gap × traffic:
    • Collection page (8.7): filter widget refactor + responsive images on grid items
    • Homepage (7.5): hero image responsive variants
    • PDP (6.0): hero image responsive variants
    • Cart, search results (2.1 each): low priority
    • Checkout, about (sub-1.0): no work needed
  3. Same fix-pattern across templates for image-heavy pages: responsive image variants via srcset, image format conversion, preload critical images. One workflow addresses homepage + PDP + collection-page-grid simultaneously.
  4. Collection page additional work: filter widget refactor (covered in psi_mobile_desktop_inp playbook). The mobile-specific INP issue compounds with the LCP issue on collection.
  5. Realistic post-optimisation forecast for the worst-3 templates:
    • Collection: mobile 48 → 70 (gap from 31 → 9)
    • Homepage: mobile 42 → 65 (gap from 34 → 11)
    • PDP: mobile 58 → 75 (gap from 24 → 7)
    • Site-weighted mobile score: 51 → 68
  6. Reading the trio with psi_mobile_desktop_lcp, psi_mobile_desktop_inp, psi_mobile_desktop_cls decomposes which sub-metric drives each template’s gap. Collection’s gap is INP-dominated; homepage’s is LCP-dominated. Different fix focus per template.
The diagnostic flow:
  1. Sort templates by gap × traffic.
  2. Decompose dominant template gaps by sub-metric using the per-CWV device-gap cards.
  3. Apply template-level fixes: each template’s fix benefits all URLs sharing the template.
  4. Re-audit to confirm gap reduction.
Rapid-response playbook:

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Sibling cards merchants should reference together

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Reconciling against the vendor’s own dashboard

Where to look:
  • PageSpeed Insights, paste each template’s representative URL; toggle Mobile/Desktop tabs.
  • Lighthouse CI, runs per-URL audits in build pipeline.
Why the Vortex IQ per-template comparison may differ from manual PSI checks: Cross-connector reconciliation: primarily internal (with the per-CWV device-gap cards and per-URL ranking cards). Quick rule for support tickets: the gap × traffic ranking is the actionable view. Don’t optimise the template with the largest gap if its traffic share is small; optimise the template with the largest gap × traffic product.

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Known limitations / merchant FAQs

Should I optimise the template with the largest gap or the largest gap × traffic? Largest gap × traffic. The product determines commercial impact: a 35-point gap on a low-traffic page affects fewer users than a 24-point gap on a high-traffic page. Why does collection page have a larger gap than homepage? Filter widget JS. Collection pages run mobile-specific filter logic that desktop doesn’t trigger (desktop usually has always-visible filter sidebar). The mobile-only widget compounds the structural CPU gap. Will fixing one template improve other templates? Some patterns transfer. Image optimisation in the homepage hero often re-uses the same image-CDN config that benefits PDP and collection images. Filter widget refactor benefits all collection pages simultaneously. Template fixes have multiplier effects. Can Vortex IQ tell me which sub-metric drives each template’s gap? Yes; cross-reference with psi_mobile_desktop_lcp, psi_mobile_desktop_inp, psi_mobile_desktop_cls. Each surfaces the per-template breakdown for its sub-metric.

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Tracked live in Vortex IQ Nerve Centre

Overall Score: Mobile vs Desktop is one of hundreds of KPI pulses Vortex IQ tracks across Website Performance (PageSpeed + CrUX) and 70+ other ecommerce connectors. Nerve Centre runs the detection layer; Vortex Mind investigates the cause when something moves; Ask Viq lets you interrogate any number in plain English. Start for free or book a demo to see this metric running on your own data.