How do you prove that a Technical SEO implementation caused an improvement?

Define:

Hypothesis

Improving internal linking will increase discovery of commercially important pages.

Implementation

Change links on a defined group.

Measurement

Compare:

• crawl frequency;
• indexed status;
• impressions;
• clicks;
• conversions.

Where possible, maintain a control group.

Also document other changes occurring during the same period.

SEO attribution is rarely perfect, so avoid claiming causation merely because traffic increased after deployment.