Direct answer: what to compare before and after a core update
The best comparison is not “before vs after” in a vague sense. It is a controlled, matched-window analysis of search engine statistics before and after a core update, using the same days of week, similar traffic conditions, and the same reporting source.
The 3 metrics that matter most
- Clicks: shows whether search demand is translating into visits.
- Impressions: shows whether your pages are still being surfaced.
- Average position and CTR together: show whether visibility changed and whether the SERP presentation still earns clicks.
Recommendation, tradeoff, limit case
- Recommendation: compare clicks, impressions, CTR, and average position together.
- Tradeoff: this takes longer than checking one trend line, but it reduces false conclusions.
- Limit case: if your site had a migration, major content refresh, or tracking issue during the same period, the update effect may be too confounded to isolate cleanly.
How to define the pre-update and post-update windows
Use a pre-update window and a post-update window of equal length. In most cases, a 14-day to 28-day window on each side is a practical starting point. If the update rollout was long, extend the window only if the site’s own changes were stable.
A simple rule:
- Pre-update: the same number of days immediately before the update began
- Post-update: the same number of days immediately after the update stabilized enough to measure
What counts as real change vs normal volatility
Real change usually appears as:
- consistent movement across multiple related pages
- repeated shifts in the same query groups
- a pattern that persists beyond a few days
Normal volatility usually looks like:
- isolated spikes on one page
- one-day drops that reverse quickly
- movement that is not visible across segments