Link Valuation & PageRank Essentials

Every newly-created web page receives an initial, very small amount of PageRank (PR).
Additional PR is accumulated through incoming hyperlinks.
Voting/flow model
- A page with PR $x$ is allowed to “vote” a fraction $f(x)$ of that value to the pages it links to.
- That voting power is split among all outgoing links from that page.
- Simplified example shown: two outgoing links ⇒ each receives $\tfrac{f(x)}{2}$ of the page’s voting power.
- In practice, distribution is rarely an exact split; placement and prominence of the link can slightly shift the split.
Iterative nature
- Links can form loops (e.g., Page A → Page B → Page A) causing PR to recirculate.
- Calculating final PR therefore requires repeated iterations until the entire link graph converges to a stable solution.
- Search engines solve this at web scale (hundreds of trillions of pages).

Google’s historical browser toolbar displayed a green PR meter.
- Not the same as true internal PR; it was a logarithmic representation.
- Approximation: $PR<em>{toolbar} = \log</em>{10}(PR_{real})$ .
- A toolbar value of 6 is ~10× stronger than a value of 5.
Toolbar PR was page-specific, not domain-wide.
Google no longer updates this public metric; any visible number is obsolete.
- Key takeaway: do not rely on toolbar PR for modern SEO decisions.

Q1: Which is more valuable—10 000 PR-2 links or a single PR-7 link?
- Logarithmic math: $1\;PR7 = 10 \times PR6 = 100 \times PR5 = 1\,000 \times PR4 = 10\,000 \times PR3 = 100\,000 \times PR2$ .
- Therefore one PR-7 link ≈ 100 000 PR-2 links.
Q2: 300 PR-5 links vs. 5 PR-7 links?
- Five PR-7 links still outrank 300 PR-5 links using the same 10× rule of thumb.
Moral: one link can be worth millions of times another; sheer quantity rarely beats true authority.

Moz – Open Site Explorer (OSE)
- Page Authority (PA) – Moz’s PR approximation for an individual URL.
- Domain Authority (DA) – Moz’s overall authority estimate for an entire domain (Google does not have a native “domain PR,” but this Moz metric is useful).
Majestic SEO
- Trust Flow – quality/authority signal based on a seed set of trusted sites.
- Citation Flow – raw link popularity metric.
Ahrefs
- URL Rank (UR) – strength of a specific page’s link profile.
- Domain Rank (DR) – overall strength of the domain.

A link’s subject-matter relevance strongly impacts its weight:
- Example: Page about “used Ford Mustangs.”
- Link from a casino site ⇒ very low topical relevance.
- Link from Car and Driver magazine or a Ford-related site ⇒ highly relevant; search engines reward this alignment.
Within a topical niche, certain sites emerge as authorities (receive many links from other topical sites).
- Links from these “hubs” carry outsized value (“topical authority”).

Authority Metrics (quantitative)
- Prefer higher Moz DA/PA; supplement with Majestic Trust Flow & Ahrefs UR/DR.
Logarithmic impact
- Remember approximate 10× jumps between “PR levels” (or their modern metric analogues).
Topical Relevance (qualitative)
- Match between linking page’s subject and your page’s subject.
Link Placement & Context
- In-content editorial links generally pass more value than sidebar/footer links.
Overall Heuristic
- Weight DA the highest, PA next, then check topical match.

PageRank is still calculated internally by Google, even if public PR is gone.
Authority of the linking page (and domain) + topical relevance ≫ sheer link count.
Third-party tools (Moz, Majestic, Ahrefs) provide practical proxies for evaluating link strength.
One must judge links on a logarithmic scale; strategic acquisition of a few high-authority, highly-relevant links often outperforms mass low-quality link building.
Next lesson will dive into link building strategies—how SEO professionals ethically obtain valuable inbound links while staying aligned with search-engine guidelines.